@BillRM,
It's only simple if you don't know what's going on. Syria has a majority Sunni population, they will not accept Assad, especially after what they've been through, regardless of how he behaves in the future. A lot of them would rather have IS, who target Christians, Shias, Allawites, Kurds and other minorities for persecution and by and large leave the Sunni Arabs alone. Then you've got Saudi Arabia and the Gulf states who would still be happy to fund IS because that would increase their (Sunni) influence whilst limiting Iran's (Shia) influence.
Then there's Turkey who does not want any Kurdish autonomy to do well because it leads to calls for greater autonomy from their own Kurdish population, and possible loss of territory.
The whole situation is far more complicated than you can imagine.