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.
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.