The stats won't be removed at all, even if it is a permanent ban. If a player hacked, yes there's always the possibility of their appeal being accepted an them being unbanned, and adding this would be a little complicated. If that player isn't actively on the network adding to their stats, then there's a good chance another player with close stats could overtake them on the leaderboard as well. You may feel free to suggest this under the suggestions section of the forums, of course.
If you have any further questions, feel free to private message me.