By the time all this ends there won't be a Syria left for them to fight over. Most of the refugees who have left Syria won't go back if there is a sectarian Turkish/Saudi-backed puppet government in Damascus. And those who remain will come to resent their new idiotic rulers who categorize anyone who is not of their sect or religion as an infidel. That shit flies in Saudi land, but nowhere else.
Muslim Brotherhood militias and Islamist groups like ISIS can win battles, and their political figureheads can win the odd election or two because of how organized they are, but as they showed in Egypt, they don't know how to govern inclusively.
Any foreign-sponsored opposition that replaces the regime won't last long and will get run out. Syria will most likely become another Libya with no identifiable government in the event of Assad's departure. And it will be worse because Israel, Turkey, Saudi Arabia, and Iran all covet this territory, not to mention the U.S. and Russia will have a say in any post-Assad Syrian government.
An excerpt from, "Syria Talks Plunge Into Disarray on 2nd Day" by Luis Ramirez, Voice of America, February 2, 2016:
Fragile indirect negotiations to end Syria’s nearly 5-year conflict slipped into disarray again on their second day Tuesday, with neither side holding formal sessions with the U.N. envoy in Geneva.
Meanwhile, the Syrian government on Tuesday allowed trucks carrying humanitarian aid to travel into a rebel-held area near Damascus as a demonstration of good will. The opposition called it an “empty” gesture as long as government forces continue to step up their offensive.
The Syrian government delegation said it did not open formal negotiations as scheduled Tuesday with U.N. envoy Staffan de Mistura, saying the basic framework or agenda of the talks had yet to be established, and the process had not yet moved beyond the preparatory phase.