In the future; don't let players argue amongst each other. You're the GM and character approval is your responsibility. If a character is unacceptable for whatever reason, you're well within your right to deny them access to the IC. Therefore, it is a non-issue if you hold your ground.

As for getting people back, yeah, er... Shit-stirring has that effect. It leaves a bad taste in people's mouths. You informed him of the situation and your action, whether he wants to come back or not is up to him.