He didn't kill it. He did a good job for what the producers created. The ship had a hole in it when Sheen got nuked. The show likely would have sunk in about the same time frame no matter who was cast in THAT role.
Nah come on, the show lasted another 4 seasons after he joined. Not many sitcoms last 12 seasons so the show would've likely run its course by then even if Sheen had stayed (especially since the "half", Angus Jones grew up and left).