It took the USA 20 years to replace the Taliban with the Taliban. Point being?
Are you happy that Al-Qaeda will go on another killing spree in Aleppo, or what?
Not all The rebels are AL-Qaeda.
Assad need off himself, he's the main obstacle
Then All the different groups need to come on table for agreements and reconciliation backed by US, Turkey, Russia and Iran.
It's possible, because Russia is exhausted in Ukraine and Iran is struggling after so many high ranking soldiers Killed in Syria
Turkey have the most influence and they fund these groups and guide them when they get power.
Then all the millions Refuges can return and rebuild.