First of all Mind Control has a possess effect and NOT a charm effect. If a player charms another player, you would see it in "third person", like a pet. Mind control should put you in "first person" control of the target unit and as has been said before, that's not implemented. Look for spells with a charm effect and test those.
Second, I suppose the only cased where charmed units might get an AI is in the case when a Creature charms a Player. Ofcourse that's not even close to being implemented, so I don't know how it will look in the end. If PetAI will allow both players and creatures to be the owner then yes, charmed players may get a PetAI. Otherwise they will get a different AI designed just for this particular case. We might even decide not to use an AI but that would probably be too hacky. Keep in mind that it's not even possible to put an AI on a player currently, but we should support future developments.