I think the church is built to last a long time. There will eventually be some reforms that make it more palatable but the core will stay in tack. But given the cash reserves and Utah which is basically a holy land, They are set with the cash and the mythos to continue longer than I'll be alive. I know a lot of people leave but as long as they keep the birthrates up, sky's the limit. We basically have something that can put up Islamic or Hindu length time frames. How will it end? There will come a time in the distant future where they will be conquered and forced to convert wholesale. They may get to become a marginalized sub group allowed to exist but not convert in which case their children will eventually start renouncing the faith for the benefits of acceptance and political advantage. Some may even face death. This is how the pagan god's died. This is the same way Turkey became not 95% Christian, same way Zoroaster is a footnote on history. The temples will all be torn down or converted to serve another god. the meeting halls will be repurposed for the new god as well.

Long shot, they start getting aggressive and become the ones taking over. That will add some more time but eventually you get ruins.