It could have happened, the Hashimites had not rebelled much before the war.
If the Hashimites stick with the Ottomans through 1918, how does this affect the war and then the postwar?
This will deny us the story of Lawrence of Arabia, and make life easier for Ottoman garrisons in the Hijaz. But, I don't think the lack of Hashimite Bedouin allies will stop Allenby's campaigns to take Palestine, nor the invasion of Mesopotamia-Iraq through the Persian Gulf.
Your thoughts?