When you visit the temple, keep poking around. There aren't that many options, so it shouldn't be to hard to find it, if it exists. Alternatively... and this is a bit risky, you may be able to completely leave the religion, and then rejoin. The problem with that is that you would have to leave the priest class, and then not be able to become a priest again before the religion collapses. Do you have any other priests, or can someone else become one?
Beyond that, you may have uncovered a bug. Your religion didn't collapse due to no elders, or no priests, or anything like that, did it? If not, then maybe you have time to work out some work-around to get things back on track.
And next time, don't demote yourself from the founder's rank! :p
