Tes, we know nothing about your Dad's diagnosis, save the PSA. When the biopsy has been done you will be better informed. The injection is not a hormone boost! The reverse. The idea is to shrink the prostate so far as possible before other treatment begins. This is done by taking out the testosterone on which the PCa feeds. A big prostate means that it would be very difficult to cleanly separate the prostate from adjacent organs.
Now, you must relax and look forward with hope rather than fearing the worst. You will soon be better informed and quite possibly learn that your Dad has years of fulfilling life ahead of him. For example, nearly eleven years ago, I was diagnosed with a Gleason 9 PCa and pretty high PSA (in the 60s). At nearly 75, I'm not done yet, by a long chalk. My advice, wait until you have all the facts then plan for the future. Meantime, try not to scare yourself with worst case scenarios courtesy of Dr Google.