I don't have trouble with heels -- it's always the toes that go in mine, and at an early stage, after only four or five wearings and at a point when the rest of the sock is perfectly sound. All my socks get mended multiple times during their lifespan; I couldn't possibly justify buying new ones every time a hole appears in the toe.
(I can see that darning heels in situ *would* be a problem!)