If the Mongols came in through Antioch you're fine. There are two "bridges" where troops can walk from the western to the eastern side of the Aegean: the Hellespont and the Dardanelles. Block both with fleets and the Mongols won't be able to cross. You might lose any territory you have on the eastern shore, but you can certainly stop them from getting to the western shore en masse. I'm not sure about the later patches, but the Mongols in the earlier versions were never big naval invaders. They'd build the occasional dhow but I never saw them load troops on them to go anywhere; they'd just march where they wanted to go.