I also believe it's likely that the producers found out, booted him on a technicality (Bo Bice has a drug arrest and Scott Savol was nabbed for smacking his baby's momma, both of which are worse than punching your sister if you ask me) and told Paula to break it off.
Or maybe not. But frankly I've never liked Paula and see no reason she can't be replaced. I left this as a comment at Ann Althouse's post about last night's AI and the ABC special:
Paula should be dumped not for the scandal but because she's a terrible singer and an even worse judge of singing ability. Any number of good singers with good ears who are also nice could substitute and make the show better immediately. And it's childish and counterproductive of her to throw a fit every time one of the other judges disagrees with her. The show would be much better with someone else in her place.
She's one of the reasons I don't want to watch the damn thing anymore. Everyone in the world knows Simon's is the only opinion that matters except Paula and the increasingly nasty Ryan Seacrest, and I may be giving Randy Jackson more credit than he deserves by excluding him from that sad, stupid, delusional club. This is a deal-breaker for me: dump Paula or I wash my hands of the whole mess. Well, except for the first couple of weeks where they show the really terrible singers who think they're good. That's comedy gold.