It happens. There are several ways to exit gracefully. All of them involve leaving a simple message to a referee, explaining that you won't be calling anymore. If you think you may be able to start up again after a while, you might want to give him some ideas for some sort of "vacation" for your character (scouting expedition, trip to the nether planes, etc.). If you're sure you won't be calling back, you might give him some ideas for a suitable death. In any case, even if you can't think of anything; please do let folks (especially Referee) know when you're leaving; one of the most frustrating things on the board is when someone just stops calling, and no one who was dealing with him/her is sure whether to move on to other things or not.