Jericho disappeared in Fallout 3?

After completing the mission: Take It Back, where you have to start the purifier, Jericho disappeared. I chose to go in to start the purifier, and then when I woke up at the citadel because I have the Broken Steel add on pack, I went to Megaton to look for him and he was no where to be found. Since I couldn't find him, I tried to retrace my steps back to the purifier, but with no luck. After a few hours I gave up and decided to complete the Anchorage mission, and when I came back I went to Underworld to get Charon since I couldn't find my other companion. Now he says that he can't join me because I already have someone in my employ. So I'm uming Jericho is still alive, but I just can't find him and it's driving me crazy. Has this happened to anyone else? Where can I find him?