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.
He could, but it would be a bit like Reddit/voat situation for an independent platform. Otherwise where can he go for remotely comparable publicity? IG/FB? I don't see FB working with his style of communication and it's not as easy to embed in news as Twitter. Ig would be closer.