We have/have had a number of greyhounds and it's the one disease we all dread. DH and I have discussed this extensively and we've also taken the precaution of discussing it with our vet (who's wonderful).
My take on it is that bone cancer is very, very painful and there is (as you've pointed out) a high risk of a sudden (and agonisingly painful) fracture. I'm not a fan of amputation for osteo- it's not without risks/issues (post op bleeding for greys often happens or problems with wound healing) and at most you are likely buying six months to a year max. Generally, by the time it's in the leg it's almost certainly also in the lungs so there are mets to deal with.
DH and I have agreed that with any of ours if this is diagnosed we'll be looking at almost immediate PTS (depending on circumstances of diagnosis). For instance when a hound was having X ray for unexplained limp, we made clear to vet that if osteo found, not to wake up and PTS there and then.
We have lost one hound through sudden onset osteo and he was in excruciating pain on his last day before we could get him to emergency vet and immediate PTS - it will haunt me forever to see how distressed he was.
Personally, I would look at PTS sooner rather than later and arrange with vet for this to happen peacefully at home. It's hard for us, but I feel it's my duty after they give us so much love. As you correctly point out, this is far more satisfactory than a sudden leg break, and possibly having to travel with a traumatised dog in agony to an emergency vet you don't know as well as your own.
I realise this may not be the answer you were looking for, but I genuinely believe that there's no pussyfooting around with bone cancer - it's a bastard, you can't win. The best you can hope for is a calm, peaceful end for your beloved hound at home before the pain gets worse.