Are you on the other side of the wall with the slit in it where you first meet Z'Ant?If not, there is a way to get there. (Through the mine tunnels and using an item to pick the door.) If you can get to the other side of this wall, you may find him standing around there.
If you are on the other side of this wall, and he is indeed gone, I would revert to the old save. IMO, Z'ant is critical part of the game and can give you a lot of experience. It might be a pain to retrace your steps, but I would do it.