With a PSA of 6000, a diagnosis of advanced prostate cancer was inevitable, I’m afraid. I’m sure you know it’s incurable, but “incurable” does not mean “terminal” and there’s a wide range of treatment options available which could keep him around for many years to come.
Your dad will stay on hormone therapy until that becomes ineffective (sooner or later the cancer adapts and starts feeding on the hormones). This may be a matter of months or may be years away - there’s no way to know. After hormones stop working there are a number of other treatments that can be used.
If you’ve not already done so, I’d suggest downloading the information sheets that are available from this site. They give a lot of useful information about the different treatment options that are available. If you have any medical questions, give the PCUK nurses a ring on the Freephone number at the top of the page - they are friendly and knowledgeable.
Hope that’s of some help.
Best wishes,
Chris