My guess is that ISIS will adjust in some way. Perhaps they will make the Iraqis pay dearly for Mosul as they pull back, then wait yet again for the US to back away from Iraq, and then re-invade the Sunni area of Iraq were they have Sunni support, and humiliate the Iraqi army... again.
The Pentagon failed its "mission" to build an Iraqi (Shiite) army. Failed utterly. They failed because they were indifferent as well as incompetent, for Sunni/Shia sectarian/tribal reasons, and because of corrupt Shia governance -- and will fail utterly... again, once the US pulls back... again. And the US ***WILL*** pull back.
The wild card now is Trump. Say what you will, he has already demonstrated that he has incredible energy and is a man of action. (Smart action or stupid action -- you and history will be the judge.) -- but action. He clearly wants to terminate the serial failure of neocon policy in the Mideast, so he will do things differently. But precisely what? Can we imagine that he can succeed where all the foreign policy "experts" have failed so catastrophically? Most people, including all those "experts" would likely say no. But all those "experts" also scoffed that he had no chance of winning the presidency. So who is now willing to be so very sure again, only to turn out to be so very wrong yet again?
One thing is certain: he won. he's the President, and he's hell on wheels.
Now we wait and see.