It's an interesting, and accurate, statistic that fewer than 50% of men with prostate cancer die of prostate cancer.
Hormone therapy is not curative, but it can keep cancer at bay for some years. Not forever, alas. But then, more than half the men who have RT will eventually get a recurrence of the disease.
It's all about time. Being realistic, at 75, I reckon your husband can afford to leave out one treatment stage and enjoy a good while yet, and I'm sure many would not even have been offered RT at that age.
But having just completed my three years of Post RT hormones, do watch the side effects. I found they got easier over the three years (though this is hindsight, I didn't notice so much at the time!), while some people find they get worse. And the energy-sapping and depressing elements are long term effects. You and your husband need to remain aware of how it's affecting him, so that you can deal with any problems arising.