For several reasons I won't explain here, I don't think it would work to simply expel him, wait to see if he sues, and then reinstate him and assert lack of standing.
cool appreciate the insight
You want to know the reasons?
I'd honestly be curious
I'm trying to gum up threads less with legal stuff, but "capable of repetition yet evading review" and "voluntary cessation" are two related examples of exceptions to the general standing and mootness doctrines. On the former, the idea is that some injuries are necessarily transitory in nature and likely to become unredressable before a case can be finally decided (Roe v. Wade is the classic example). On the latter, a defendant should not be allowed to manufacture mootness by ceasing its bad conduct once a suit is filed only to turn around and do the exact same thing once a case is dismissed as moot. Otherwise, the offensive conduct could never be addressed. Some other stuff too, but I don't want to get into it.