I'm not clued up enough to offer a solution to this.
However, Frederick Forsyth proposed as follows; -
Partition.
an enclave in western Syria (Shia and Alawite) under Assad.
an enclave in Northern Syria alongside Turkey (Sunni).
an enclave in Southern Syria alongside Jordan (Sunni).
Citing previous partitions: -
Christian East Timor/Muslim Indonesia - no more violence
Bangladesh/West Pakistan - no more violence
Czech Republic/Slovakia - co-operating as members of the EU.
All former Yugoslav provinces now living in peace.
Better than endless war and terrorism?
Your thoughts.......?