Kazzy, oh the perils of Dr Google. We can all search for worst case scenarios and scare ourselves half to death. That doesn't help at all. How long on HT? Well, I have a cousin who has been under treatment for 20 years. Nobody can answer your question, because it all depends on the individual. In my case, it worked for a few years before other treatments became necessary, but I still have 12 weekly Zoladex jabs 11 years on, because they provide some benefit; not enough on their own to keep the PSA low but useful anyway. There are lots of different scenarios for the use of HT, as I hope I have shown.
Your OH has had a very good initial response to HT. The PSA will probably continue to fall. Hold on the the facts and stay positive.