Mr. Assad is going to lose his war - and his life - as he deserves. But what comes after him will no doubt be worse, unless Russia intervenes to ensure the continuance of a military dictatorship under their influence and patronage. McCain, et al, will want to use US forces to counter that. We must not let them, for that will be the gateway to WWIII.
After? There can be no conclusive after, just lots of failed attempts at closure. Power struggles, proxy wars, attempted partitions, ad infinitum. Syria is too severely f@#$ed up for any afters.