I scroll through my friend list sometimes to look for something to do and see a lot of "deleted" accounts, not knowing who it was, and where they went or why.
A deleted name is one of three things:
a) Transferred to another server.
b) requested the account be closed permanently
c) got banned

Out of those, A and C will be more than likely since most people who quit a game aren't going to take the time to call up SE and ask them to close the account. They will just stop playing.

If it was A then that person didn't quit, they just moved. If it was C than more than likely they were cheating in some way and that to me is better than them still playing.