
Siege of Acre (1799) - Wikipedia
What if the French got lucky - suppose they breach the outer wall early in the siege, before the defenders have time to build a second one - and took Acre in 1799? While the fate of his campaign was sealed the moment the fleet was destroyed at Abukir, where else could Napoleon go with Acre under his control for the time being? Would a French conquest of Jerusalem have any major religious and political consequences, however brief it may last?
A possible, nasty side effect (for Napoleon) is that he might get trapped in Palestine and Syria if he stays there too long: an Ottoman army landed on Abukir in July, and if he's still in the Holy Land by this time they might be able to retake Cairo and Alexandria before he can help the French garrisons there.