Very disappointing news, as Dennis has long been one of my favorite players to watch.
That said, if he didn't break the rules, I'm sure he can get it fixed by an attorney. If he did, and there were no extenuating circumstances, such as illness or bereavement, any trouble that comes his way is on him.
I would rather an exception be made here, but if Dennis has violated the terms of his being permitted in the United States, he has done this to himself, and you can bet your last dollar that he knew the exact terms of his visa. Customs laws concerning immigration and visas need to be enforced rigidly as doing so is a matter of national security.
I hope it turns out that Dennis didn't break the rules, but it seems unlikely at this point. Guess we'll see. Hoping for the best.