See I'm thinking he was already degenerating and if they hadn't gotten the boys out of him he would have turned into a five year old. Tuvok would have thought of leaving the ship, he already had control access at his station to stuff. He would have set the ship into some kind of lockdown mode, grabbed a shuttle and fled, probably rigging up a cloaking device while he was at it. Tuvok's smarts and Neelix's desperation.
I saw a dead-fic that started like that. That would have been a way more interesting episode. Much better than the Mr. Perfecty-Perfect-Pants we got. It's like they were saying "Look audience, Tuvix is perfect! Care about him!"
This ep was a lot less depressing and a lot more creepy when I tried to wrap my mind around the state of having your conciousness taken and used while youre still alive, or not, and then you're in a foreign body, but it's like your child, but they're you, and someone else at the same time, and so you aren't yourself anymore.