Numbness after many years? Still numb over scar area from appendectomy after more than 10 years. Will the numbness ever go away?

At. At this point probably not. We have many small nerve fibers that enervate our skin. These nerves are very small and not seen during surgery unlike the larger nerves that control your movements. Incisions that run horizontally (hernia incisions, appendectomy incisions) may cross these nerves and cut them. Some of these nerves may regenerate slowly (over a period of months) and some do not ever fully regenerate. It does not cause any physical debilitation but it can be odd to have a numb spot. After 10 years it is very unlikely that sensation in that location will return. You are definitely not alone though, many people have numb areas over there scars.
No. If sensation has not been restored after a year, it is unlikely it will ever.