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.
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.