200 BC? I doubt Alexandros would live till then, no one can live so long, and IMHO the diadochi war is a “scripted” stuff that happens after the Alexandros death. Also Rome had Marcus Valerius Corvus, when Alexander started his East invasion. Romans were not green, they were very experienced in different Italian conflicts, also they already had Camillian-style army, as Camill lived before. Italian locals helped Carthage coz they fought with Rome particularly, Rome was an enemy. Alexander would come for the whole Italia. Could samnites prefer Macedonian rule instead of Roman, choosing which side to take? Never trust the ally with someone who more powerful. Rome was not a master of some parts of Italia, so there Alexander could’t be estimated as Salvator, coz they were independent, and their independence would be threaten. That is why they would ask someone to help. Whom? Rome.
I wonder who had the best fleet then? Carthage or Macedonia? If Carthage, then Mak army wouldn’t have supplies.
The same stile Roman army beaten Pirrus, who lived later, had even elephants and Mak-style phalanx was improved. Alexander would find his own Vietnam, and he should forget then about East. I sow in Wiki that Pirrus invaded with 40 thousand poople including elephants, and Alexander had 37 thousand invading Asia Minor. The difference is little.
After conquering India? No way. His army was demoralised. No one wanted to continue the struggle. His elites wanted home to their families. Alexander was frustrated by the death of Hefestion. And who said that he could conquer India peninsula?
The news that Alexander led his army to Roma would reach the Romans. It wouldn’t be surprise.
And what would eat all these army there? And if the Carthage cut them supplies by sea, Romans burned fields, and avoid general battle as it was some years later with Carthage? What then? His army would collapse like the Colossus on the clay legs.
USA (!) stacked in Vietnam, Iraq and Afghanistan.
«Alexander, we made a long trip from Macedonia to India, then from India to Italia, we just want home, we haven’t seen our families for more then 10 years. Lots of us died on the battlefield, from diseases, even old age. Alexander we want home!» - would heared he.
BTW after India he should hear about China and go there. Who would win?