I don't know if there is a great answer for this, but variations on it have come up in past and maybe something at the links below might do what you want.
https://mathematica.stackexchange.com/questions/8753/finding-a-concave-hull
https://mathematica.stackexchange.com/questions/50742/meshing-the-surface-of-a-non-convex-object
https://mathematica.stackexchange.com/questions/88752/delaunaymesh-in-a-specified-closed-region-creating-a-concave-hull-from-a-set-o
