This guy will probably end up like Qaddaffi & Syria will be ruled by the very extremists we were supposed to be fighting.
Assad can’t regain control of Syria without killing the majority of Syrians. Whereas he is just the guy to do that, he doesn’t have the means, hence, there will be no military resolution to his problems.
He has consistently refused to negotiate on the same kinds of flimsy pretexts used by the PLO and its spinoffs, and the Russians and Chinese will veto any kind of UN Security Council resolution, so there will be no negotiated settlement to this.
The various paramilitaries don’t have the means to control the entire country either, but the fighting will go on for years, and will continue even if Assad is bumped off at some point.
None of the militia groups (there are many) will ever exert control over more than some little fiefdom, so the eventual disposition is partition, and probably after the fashion of Lebanon, which was dismantled with the connivance of the PLO and Syria, and the active participation of Iran and its proxies.
Meanwhile, the Russians will continue to dig themselves in deeper, and similarly, the Iranians will continue to pour manpower and treasure into keeping Assad propped on his horse.