If they can detach just half of this because of allies they could consider a push down the Nile toward Sudan. Better than going west across the desert and more Mongol expansion.So in ATL the Mongols win the Battle of Ain Jalut. They do not lose this army. And we know that this army is not needed to pacify Mesopotamia and Iran (and the Caucasus and Anatolia and other parts) as they had sufficient Mongol garrisons.
- Where can the Mongols use this army?
- Right. This army would occupy Syria/Levant and Egypt. 5-10 thousand in Egypt and 5-10 thousand in Levand would be more than enough.