GURPS San Tomas plausibillity check

The Mongol invasions continue their seemingly inevitable course. European refugees fled to the Crusader States in Palestine, giving a big demographic boost and, by allying with the Mongol Ilkhans against the Muslims, the Crusaders survive and flourish, seizing Egypt in 1380 and sacking Mecca in 1409 with Venetian ships built on the Red Sea. In 1580 sailships from Crusader Egypt dominate the Indian Ocean as England reconquers Europe from the White Horde.
Plausibility?
 
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