What are your favorite strategies in fixing post-surgical depressions from facial flaps?  

A depression is a 3-dimensional contour deformity. Depending on the size and location likely the area will need to be excised, followed by wide-undermining (or another flap if need be) then reapproximated with good eversion. Others may have more experience with fillers/fat grafts but I do not.

Dermabrading and derm-sculpting are most helpful when your have too much tissue and you are trying to decrease the convexity. When you already have a depression it can make it worse... Theoretically, you could sand the sides to make the depression less acute and possibly less noticeable but it won't...