The pastor himself decides when to leave/ where to move on to. When he leaves, the elders (people who have done a lot for the church [rarely in a monetary way, they don't just buy their way in]) get together and start accepting applications from different pastors, trying out the ones who look good, then they hire the one they can come to a consensus on. The guidelines are not who can attract the most people, but the one who stays true to the actual teachings of Jesus without adding their own crap or deleting stuff they don't like.