I have members who ask to terminate their accounts - my usual response is just for them to change all their alert prefs and log out.
But many people honestly cannot help themselves. They want to stay away, but can't. If you ban them, other members consider it negative.
So my suggestion is for some softer descriptions to be allowed, although most of the functions would be the same. It might involve other members getting a "member has asked to be on hiatus - we don't know when they will be back" or even a "member is deceased, sorry" message.
Has something of the sort been suggested before?