I thought you could retreat to the plane at the end of time but when you wanted to come back, you needed to return to a "checkpoint". This prevented the in/out strategy, particularly against boss. If you can warp at will and return like you never left, there is no challenge if the boss doesnt instakill you, which isn't fun.
Personally, I don't mind if there isn't some mana regen. I just wanted to know if "pure mage" was a viable build and possibly fun. And sure, we have potions which will help.
