It's good that they're taking your case into consideration, especially because you provided proof of your intent to return to the game. I don't know if they can guarantee boosting you to Legacy status because just logging back in doesn't mean you would have stayed for the 3 months. I'm sure you would have, but without any certainty from their perspective I don't know if there's a lot they can do. Maybe they could ask for any remaining monthly fees that would bring you up to the ~$30 minimum. (You might have paid for 2 months, so they'd ask for a 3rd.) In any case, I hope it works out.

As for a whole department on this issue, I don't see any reason not to add a couple of specialists temporarily for this sort of thing until launch. It sounds like a pretty rare case, and not everyone with the issue is going to call, so I doubt there'd be any need for a full team. They'd have to spend more time with each person, though, just to verify everything... I don't know. I just wish SE support was more responsive as a whole, so maybe we can make an example of this case to get them off their asses.