LMsA: And it opens up all his tweets to responses that can be read by everyone
That's the first thing that came to my mind- he can leave Twitter if he wants, but he'll have to delete a whole lot of his tweets first. Otherwise, people will be free to reply to his older ones and dump all of the skeletons from his closet for the world to see.
I don't think he has the patience or energy to delete literally hundreds of tweets (possibly thousands). And I know it would just kill him to delete his account. His only option is to pray to Jehovah (or sacrifice a chicken to Elon Musk) that X decides not to make this change.