WI: The Mamelukes of Egypt are defeated by the Mongols at the battle of Homs and Sultan Qalawun is killed. Will the Mongols go on to conquer Egypt and even extend their empire into N. Africa?
Possibly Egypt, but I doubt much further- overstretch will start to kick in. Is there any chance of the Mongols restoring the remaining rump Crusader states to the region as loyal vassals?
That depends on whether the Crusaders change sides again. If they do then the main payoff would be the Mongols keeping the Muslims off their back. On OTL after Homs the Muslims launched a series of campaigns against the Mongols and when they did not find any they would carve another slice off Outremer.
Of course the Pope might question the Crusaders doing business with Nestorian heretics, but then he is in Rome the King of Jerusalem is in well Jerusalem! Any cleric who kicks up a fuss could very well be kicked out of the realm.