Is it possible that he doesn’t serve a full term, sure.
Bernie Sanders already had a heart attack, and Trump has himself been under extreme pressure this last month.
If it looks like Trump is still a threat when it comes to decision-making time, there’s going to be more pressure on Michelle Obama to run as VP, especially if Mark Cuban throws his hat in the ring. The likelihood of either happening has to less than 10%, though. Of course, that kind of complacency is how we got here in the first place, the Clinton campaign’s arrogance in trying to expand the board instead of protecting WI, MI and PA in the first place.
At this point, the only thing that really matters is which administration (or future one) was is more dangerous to the health and prosperity of the United States...to me, it’s not even a close call.
The fact of the matter is that with Tillerson, Mattis, McMaster, Kelly, Cohn, etc., all gone...the guardrails are completely off and there is just nobody he will listen to other than Ivanka and Jared Kushner. Eventually, a foreign policy crisis will arise and there will be nobody there with any degree of governmental competence to provide a counterweight to the President’s worst, most aggrieved impulses.