Syria is a Baathist regime, no dissimilar to Irag under Saddam. A feature of this type of regime is that it doesn't allow opposition or alternatives, and so if it collapses there is nothing to replace it, and chaos ensues.
It is now widely accepted that the lesser of the evils in the aftermath of invading Iraq, would have been to allow the lower level Baathist commanders to continue to run the state machine ,with some oversight from the U.S. or UN for the short and medium term.
So my theory with Syria is that the West should try to do a deal with Putin, where his sphere of influence there isn't compromised, but he delivers Assad and his generals to a war crimes tribunal, but his lower orders continue to run the state with Russiioan supervision.
Also access must be given to UN inspectors to ensure no slaughter of innocents by any of the factions concerned.
Probably unlikely to happen , but the alternatives are to ignore it and let things get worse, or risk a U.S.(and the West) war with Russia.