I'm truly sorry to hear your dog has hip dysplasia (fine looking animal BTW). You haven't said what hip score rating he has but it's obviously serious if you are contemplating femoral replacement surgery.

One of our dogs has slight dysplasia and he was prescribed a 6-month course of calcium tablets. Touching wood, he's not shown any signs of dysplasia to date - this merely showed up on a cautionary hip x-ray for unrelated lameness. So far, he's not experienced any directly related problems but to be brutally honest I expect they might catch up with him later in life.

Personally, I would seek a second vetinary opinion just to get a (possibly) broader set of options in all respects. I'm mindful of the faith you have to place in a vet' when you trust them with your animal and I'm in no position to doubt them but considering this is a lifelong ailment it's what I would do.
In our situation, because ours was a youngster (like yours is now) we were in-time for the calcium to be a worthwhile treatment. I'm not suggesting all you need for Derby is a simple course of tablets (it sounds worse than that) but while you have a growing dog make doubly sure you don't miss an opportunity.