TP was, in effect, disabled at the area where the ancients resided. It's been done before, with half-successful results; the player could just TP right before the ancients anyways.
It would be trivial to code an area that can't be entered or exited after a quest is 'activated'. The Ancients thing was coded sloppily, simply resetting if someone uses a town portal while they're there. It wouldn't be hard to really code something like that, though.
This might be something that's been suggested a ton of times before, but I've never seen it...it just seems like a likely outcome if you have those health orbs that drop, but there are still potions in the game (as far as I know, both are true according to the latest news).
What I think they may do is make it so that you can buy potions in town, but no potions will drop from mobs, just orbs that'll heal you some, but that you obviously can't carry with you. In this way, potions will become more of an item for emergency use.