Are there any combat styles or AI packages that can account for team fighting, specifically for NPC's vs. NPC's? Would it be possible to set up a scenario where if it was a 3 vs 3 NPC battle, the NPCs would fight efficiently? For instance, if one fighter got to low health, he would hang back a bit and heal up before engaging back in the fight? Or if two melee fighters would protect a third mage, who in turn would heal and dish out much of the damage?

If this could be accomplished with scripting, does anyone know how hard it would be?

Unfortunately in this game as with many such Melee combat games the AI is really only set up for a "free for all".

Even with two groups of the same factions and positive dispositions to their team mates they will not follow good group tactics. The biggest offense is that they will not hold a formation with each other.

Scripting can help a little with a few aspects such as not shooting each other in the back with arrows as I have done so with a combination of scripting and combat styles swapping but it required a Hell of a lot of very tricky scripting! See my Hammer Blade mod on TesNexus and look at my AI scripts for the Duke Patrick Oblivion character and his squires for some clues.

I would not hope for much on this however as the core combat directives of the AI in this game is "every man for them self."