From my experience, as long as the follicles are present, there is a good possibility of them responding to PRP and Acell. This can help slow down and reverse some of the miniaturization of the follicles. I've found that it works better in younger patients than older patients.
Everyone will respond differently to any treatment. If you have concerns see your doctor for an exam. Your doctor can better give you an assessment of your condition and treatment options.
In my experience, the hair that is completely lost is lost and gone and will not respond to treatment with PRP. The hair at the hairline will respond by thickening and reversing some of the effects of miniaturization. Acell is a foreign material. So long as you understand that there is a risk of allergic reaction then it will potentially increase the duration of effect from the treatment. In males, I like to treat for 3-4 treatments stacked within 2 months of each treatment to maximize benefits and response seen.
In my opinion, the temples are an excellent area to inject with PRP. The response that I see to PRP is related to the length of time that you have been losing or miniaturizing the hair in the affected area. If the hair loss has been longer than 3 years, it is difficult to predict how much regrowth will be possible. PRP is excellent at decreasing hair loss and thickening the existing hair. The amount of regrowth is harder to predict. I am NOT a big fan of adding Acell to PRP. There are no definite studies or documentation that it provides any benefit other than for hair transplantation. Furthermore, it acts as a foreign protein and can cause adverse side effects. The duration of activity of PRP alone has been reported to be anywhere from 4to 12 months. If you have a strong genetic history, it will need to be continued. Hope this helps. Good luck.