How long does a facial fat transfer generally last?

All very good questions. 
1. A portion of the fat will live forever or at least as long as it would have lived where we harvest it from. 

2. Yes, local with some oral anti anxiety medication as needed in my hands. Patients do markedly well. 

3. In my hands, patients obtain the best results when we plan on two transfers over 6 months. Overinjection is required as only a portion of the fat will stay. With surgeons that do this a lot, it is not really over injection as we plan for a certain amount and that is what we inject. But from the patient standpoint it will appear over injected for 1 wk. 

4. I prefer cannulas for two main reasons. First it is safer; the likelihood of injections into a vessel is lower. Especially with cannulas 22g or larger. Secondly, it let's you put finer fat in precise locations and levels of tissue. We are able to thread the fat into its appropriate position this way. 
Hope this helps.Best of LuckDrC

Fat transfer to the face has a variable degree of longevity.   In some cases the fat remains permanently and in others it can resorb after several months.  It can be performed with the patient awake using local anesthesia.  Small cannula’s are used to harvest the fat and inject it. 

Fat grafting is very effective for long lasting results. Yes it can be  done in the office under local anesthsia. I would suggest finding a board-certified plastic surgeon who is very familiar with grafting techniques for your best results. Once a tissue such as fat has been grafted it is a permanent material. As  you age that fat will also likely subside and therefore, down the road you may need more. As far as over grafting, all surgeons will essentially put in the right amount to get the shape they're going for and therefore will likely use more than is needed initially.Best of luck! Dr. Boschert