I wouldn't unban anyone.
They violated the ToS and the ToS clearly states what would happen if a rule was to be broken. Plus, if they could get unbanned, people would start making up excuses saying why they should be unbanned and anyone else can use that excuse.
just my 2 cents
If i were Treyarch, i wouldnt put down the ban hammer. I would just reset their accounts to level 1. Bam, problem solved. No more whiners about "wtf i got banned" when they just get reset and can still play the game.