This would be where the current pet system could kick in. The NPC henchmen would then be assigned as someone's pet with limited commands - basically Heel, Guard, Place, and Sic. The rest of the pet's abilities would be AI controlled; I've played both SCH and SMN, and while the pets aren't as good as players with managing their abilities, they're not complete rubbish, so it's better than not being able to finish the instance.

Just a thought. There's been plenty of times where I've let Eos do the majority of healing on a boss fight and done DPSing or had Titan tank a boss because the tank disconnected, and it might cut down on the frustrations of late night/off-prime time hours players who get stuck in an instance where the DF never gives them a replacement.