He's not moving anywhere and any Twitter controversy gets more people to tweet about that controversy... Until he forces a significant part of his followers to leave, it's not a bad situation for Twitter to be in.
Or worse, in terms of discourse. I suppose twitter is awful for something as complex as political debate, but removing an entire half of a political spectrum would only serve to further divide our country, something which the real demagogues of the world would love to capitalize on.
I would suggest that maybe Hillary Clinton's campaign and candidacy alienated many people in the center. In my mind, that seems to be the simplest explanation for the existence of Obama-Trump voters.
Removing Trump would not remove entire half. (Assuming there's even a half) Some would move, majority would be just fine with occasional screenshots from another source, and lots would find a different celebrity to follow.
They're not half of a political spectrum. I can get on fine with most conservatives despite disagreeing with them, but Trump's most vocal supporters are part of a cult of personality rather than a complex polity. The divisions are already there, all the appeals to reason and fellow feeling have been exhausted.
I think the Obama-Trump voters were a result of 8 years of partly empty promises. (He did a lot, but people hoped for much more. Yes we can / yes we scan.)