And here goes my version, yeah, rather than talk about Grandpa's paradox, maybe we could think about Fry's paradox (killed his own "supposed to be" grandpa, and become his own grandpa X) )

0. I assume that Rome will still exist in some time, but the difference starts when the Celtic raids to Roma proceed to exterminate every one of them, so no Rome.... and at later times, the Samnites will dominate and take all Italia.
1. With no regional powers exist to threaten Magna Grecia, Pyrrhos will never go to Taras, and after he was expelled from Syrakousai, he will set himself to the chaotic war of Makedonian succesion earlier... and because of his genetically inscribed bad luck, we can assume that he will try to attack Pella, and get a Phyrric victory there.... and leaving Epeirote military in really bad condition.
2. With Epeirote weakned, Kardechoi will take all Iberia, because no one except Iberians care, and they will just trade and exploit Iberian wealth for quite some time, anbd rebuilding their army for eastern conquest.
3. With the Weakned Epeirote and Makedonia, Koinon Hellenon under the leadership of SPARTAAAA, will proceed to liberate most of Greece.
4. The Ptolies will constantly at war with Seleukeia, and this weakned both of them to some extent, while Baktrians and Pahlava start growing in the east, holding Saka incursions.
5. The Makedonians and Epeirote, frightened by what will Sparta do to them, as they are still weakned in some extent, made alliance each other, and holding the United Greek States' Growth at Thessalia and Thermon. After that tiresome period of Wars, the three factions will be exhausted, and seeking to build rather permanent peace treaty for them, effectively dividing the Peninsulla into 3 Regions, and allied themself to each other (despite some Spartan's displeasure, heck, that was Athenian philloshopers and Rhodian politicians that do the Peace confrence). The northwest and Illyrian lands will be Epeirote suzerainity, the northeast will be Makedon, and the south will be Koinon Hellenon, and they made a promise, if any of them break the treaty, the 2 others will ganged up and smack the violator, in front of Zeus. And that will be signed by Pyrrhos, Antigonos, Areous, and Chremonides. For a long time they will obey the treaty.
6. Pyrrhos will try his fortune on Conquering to the North, he will be on tough fight against the Boii. The boii will fight fiercely to defend themself, but as Sauromatae raids their easternost part, and Getai chipping their southern possesions, Boii will be conquered by the Epeirotes, and Pyrrhos will passed away peacefully because old age... after taking much of central europe.
7. The Makedonians will be stagnant, defending themself against Thracian incursions under Lysimachos, but fight valiantly enough, as Epeirotes and Hellenes will occasionally help them... and will be little changed.
8. The KH on the Other side, will made overseas "Liberation" attempts, and directly invade Italia because the Samnite league start to enroaching Magna Graecia and even defeating Syrakousai... the defeated Syrakousai will cry for help, and after that, what will happened is the Samnite vs KH wars. Because the Samnites didn't have the same commitment as Rome, they will be reluctant to use all their powers, and will be defeated. All that left afterwards will be Federation of Megale Hellas, backed by Sparta and Syrakousai, Holding the Kart- Hadast Enroachment in the East, and they will try to defend Hellenic cities as far as Emporion and Massalia.
9. Basically, Karthadast will reign supreme on Iberia and Northwest Africa, while Koinon reign in Italia, and Southren Gaul for a long time, without Rome, Aedui will be defeated, and Arvernii will rule the rest of Gaul. Sweboz will raid north Italy occasionally, but the Hellenes and Epeirote will be able to check them in place.
10. The Seleukid's Persian possesion will fall to Pahlava, while Saka will trample Baktria and conquer India, but left their Baktrian holdings largely untouched. Ptolemies will claim much of levant, and Seleukid will be mostly on Babylonia and Asia Minor possesion. Pontus take the Cherosonessos, and made themself master of Black Sea, and Hayasdan will be still peaceful Hay Kingdom, uniting all the Hay and keep Sauromatae in Check.
11. And all will be much the same for a long time, as the World balance itself...
12. In the verge of what means the Judean rebellion... the Ptolemies' garrison was expelled from Levant, and a Jewish state was founded.
13. Lacking the Battle of Magnesia, Seleukid manages to endure heavy palace intrique, and after a drastic dynastic changes, they start to reclaim much of their lost lands, and take back Persian lands, beat Pahlava, put baktria back into satrapdom, and Hold most of asia Minor except Pontos, The KH, feels threatened, attack Asia Minor for the fear of Powerful AS, but find themself on the losing ground, soon, the entire KH Makedon, Epeirote alliance fought for their live against Seleukid infasion of Greece, and they failed rather Miserably... AS will take all makedonia, Southeren Epeirotes, and made all hellas client states and divided. Then, they set their eyes toward Syrakousai and Italia, invading them with their massive manpower and take most of their land under submission. Epeirote royal family was saved because they move to Boii lands, and allied themself with the Thracians for the fear of Seleukid Incursions.
14. and feeling threatened, Karthadast attack Italia, but as the Anti Barcid dominate their senate, they will be unwilling a bit, and generally just a minor naval skirmishes occurs. The two empire AS, and karthadast is at war with each other, but they are at stagnant position.
15. and we'll see a big Seleukid Empire, sprawling from Italia, Hellas, Persia, and India... while at the levant, the Judean state will allied themself to Ptolemies out of fear with Seleukid Invasion...
16. And hear Judea allied themself with Ptolies, Seleukid invade them, and put them into the Submission once again, supress them, and Invade the unwary Ptolemy kingdom.
17. And the Seleukeia hegemony grows larger and larger, now defeating Ptolemies and taking entire Egypt as well...
18. And as it had been written before, Jesus was born in Israel... but now, he was born when Antiochus 19 order the census of the entire world.
19. He then teach as what the bible said, and the Pharisee didn't like Him as usual... then, he was captured, and taken to the Satrap of Iudaios, Pharnakes Philatos... and while the Satrap couldn't find anything wrong with him, the pharisee said that he want to be Basileos of the Iudaioi, and for that, the Satrap wash his hands...
20. And then Jesus was crucified, a miracle happened as he passed away, and earthquale, as well as darkness ensues.... a Strategos that was charged to oversee his execution, and seeing all the signs, knelt himself before Jesus, and said "I know that this man was really a Son of God"
21. The Satrap order his men to guard the Jesus' tomb, but on the sunday morning, the Pezhetairos guarding his tomb are shocked to see Jesus was risen with bright light comes from him... because they are not Romaioi who run away... they decide to check what's happened, and found that Jesus was allready risen.... and they seeing him alive, folding his shroud, and they ask.... "Did you really son of God?" and Jesus replies "As You have said..."
22. And then Mary and the women comes, found Jesus was alive and all Pezhetairos that guarding his tomb was knelt before Him... they are so joyful, and spread the word of it, of course, the Pharisee still want to cover the news, but as that news spread, the Satrap personally comes to check if Jesus was really alive or not, and in his way, Jesus suddenly appeared before him, and said that God forgive what he has done before...
23. And in the 40 days, Jesus is going back to heaven....
24. The Christianity spread rather wildly... and in turns, the Arche didn't like what happened, and start to prescute the Christians.... and Christians fled to the west, to the land of Kart-hadast... and still persecuted because they refuse to bow for Baal... of course, the only way left to live peacefully was the Arvernii and Sweboz land, and they go there...
25. A miracle happened, when a Sweboz chieftain fought a dire battle against arvernii force, a cross sign seen in the sky, and in this sign, he got a victory against the Arvernii, of course, that means the Sweboz become Christian, and with God's blessings, they unite all the Northern Europe...
26. Because Christianity never grows much in the east, and grows in Northren Europe instead... there will be No Islam....
27. Sauromatae also got much influence from their Sweboz neighbours, and all the Steppe will become Christian, leaving Hellenic and Kart-Hadast wolrd still in Pagan majority....
28. Because the Steppe tribes become Christian, the Xiongnu become Christian too, and invade China sucessfully, made China the biggest Christian nation on earth, and as the Sweboz in the west was defeated by then Buddhist Hellenic states, the Asia will envolve as Christian lands, and Europe as Buddhist lands.... except the north scandinavians that was still largely Christians...
29. Maya civilization then launched surprise invasion to the Buddhist hellenic Europe....
30. And The Americans start to colonize Europeans, and put the Europeans in their "European Reserve area", taking much of their land... and devastate Hellenic and Kardechoi civilization...
--------