One thing to realize is that fat injections and anything in life aren't necessarily permanent and forever.  Fat injection results can last many years if done right. Just like the fat that you had when you were younger, they eventually went away after a while as you aged. This same process will eventually happen to the fat that you have injected.  Over many years, the fat will get metabolized as you age, but the results may last for 10 years or more. 

Another option of volumizing is through facial implants. Silicone is the most common implant that people place within the face and these implants can last essentially forever. Facial implants are more of a permanent option but the drawbacks are having a foreign material placed within your face and it does require more incisions and likely recovery time than fat injections. If you can handle the idea of putting something foreign into your face this is a great option. 

Silicone implants have been placed into thousands of patients around the world and has an excellent track record for safety.