They could just kill his character off
Death by Bologna Sandwich.....
They could off him by having his character attacked in an alley. The attackers could loop a rope around his neck and pour bleach all over him, while gagging on a Subway sammich.
Time honored way to get rid of cast members that are no longer wanted - e.g Charlie Sheen fired and killed off from 2 1/2 men, Gary Dourdan fired and killed off from CSI, etc.