The only solution to war is more war.
To begin restoring that hope will inevitably mean international intervention of some kind. The establishment of credible safe havens and the implementation of a no-fly zone must be on the table for serious consideration.
Except we've really gone too far now for this to be even approaching a viable solution. Establish a no-fly zone and you undoubtedly help protect civilians, but you also give a massive advantage to the rebels, including Islamic State. It's difficult to imagine how things could get any worse, but the bloodletting likely to follow the total collapse of the Syrian government and immediate battle for the spoils between the rebel groups will be immense. Safe zones again sound like a great idea, but who on the ground is going to guard them? The Kurds, the very people the Turks have launched 100x more air strikes on than IS? The rebel groups other than IS?
Nor has there been any past argument for intervention that would have helped matters. Unless it had evolved Libya-style into regime change, the mooted response to Assad using chemical weapons in Ghouta was to chuck a few more Hellfire and cruise missiles into the mix and hope that made clear just how serious we were about him killing people with explosives and bullets rather than more exotic weapons.
The only realistic option at this point is to push for a ceasefire between the rebel groups (excluding IS) and the government, with the promise being that once the fight has been taken to IS, Assad will depart and a settlement will be reached from there. Even this would require a massive turnaround in current attitudes, such has been the amount of blood spilt and the belief on all sides that total victory can still be achieved. This I'm afraid is the fault of all involved. There are no clean hands. And taking in an extra 4,000 refugees remains a completely pitiful gesture, considering the role we've played in Syria reaching this beyond grim juncture.