I don't think balkanization in the sense of several new states popping up in the former Syria is likely at all. It doesn't make geographic sense and, apart from the Kurds, no players in the war would want it. However, balkanization in the sense of people being divided along petty religious-ethnic-social reasons has already happened. Much like Lebanon didn't turn into Maroniteland, Sunnistan, and Shiitia, Syria won't really split. No, the players will keep the frontiers the same and fight for control of the whole thing or to protect their position in it. And that will go on indefinitely, since Iran and Russia will always give Assad whatever he needs to keep things going and the Saudis and the rest of the Gulf states will give their rebels whatever they need to keep things going.
Even if, say, the rebels assassinate Assad and his "government" falls or Assad totally retakes the northeast, that just changes the phase of the war. Plenty of people will still fight the Islamists even if Assad himself is gone and plenty of people will still fight Assad indefinitely (whether they're Syrian or not) since the Saudis have made this the current jihad and Assad winning means Allah losing.
I really just can't see any way this ends, short of one side totally winning, which is very unlikely. Regardless of how the situation came to this point this is where it is now, and this is probably where it will stay unless something dramatic happens.