I've done tons of research on this and I've concluded that fat grafting is the answer to large volume loss problems. The problem is it might not be the right time to jump in and do this procedure quite yet. The good news is this procedure might be perfected in the near future.
It has recently gained massive popularity and almost everyone is starting to perform it. Many research papers are being churned out about different techniques, new filtering technology, additives such as PRP, and the list goes on. I think this means wait a couple years for things to stabilize if you can.
Grafted fat has a couple issues that aren't fully understood. Grafted fat has been claimed to behave like the donor site, and some doctors warn that gaining weight can affect the size of the graft differently than in natural facial fat. I really don't like the sound of this, but I guess if your metabolism is super stable there's nothing to worry about (again, something I want to wait for more research on). The 'take' of grafted fat is random, but many doctors claim it to be about 50-80% on average. Some say much of it is dead and that dead tissue is just walled off and slowly eaten away (which creates volume, but probably not exactly what anyone wants). Others dispute this saying that whatever survives after about 2-3 months is living tissue and will persist until aging reduces its volume. With all this in mind, it apparently has very high satisfaction rates among patients. I'm not sure what to think of doctors writing fake patient reviews, but a lot of positive reviews say it looks and feels totally natural.
Fillers like Restylane are a great alternative to fat, but I feel like it's a waste of money for anyone with more than a small volume deficiency. Restylane has a tougher consistency than fat, and I have read that it basically just sticks to the bone (which is where you want it injected). Having tried just 1cc of restylane in my tear troughs, it caused some very slight lumpiness for a couple weeks, and the when that settled the changes were barely noticeable. This means you'd need like 6-8ccs of restylane every 6-12 months to treat a moderate/severe volume deficiency.
Anyway I hope this thread stays around because I'm very interested in these procedures, and I think many people seeking jaw surgery might also have soft tissue volume issues.
If you want to PM me, I'd discuss with you some of my consultation experiences with different doctors...