DeletedUser
but on beta, you could log in to both copies on original world and migrated world. so while waiting to delete on original world, i could duplicate all items by trading them to another player.
they solved that later on the migration testing.
After getting that script that would delete your account when you asked for a migration from w3 to w1, they too made an update on the migration. So after you moved to w3, if you tryed to get into w1, a new account was created. (some people got into trouble with that one since the new account too would need 5 days to be deleted)
So, on that point i think they got it ok. The major problem, for what i could see, was with the avatars that where on a mess for the people that stayed with the old one. And that thing was not solved before they closed the migrations there.