the rogue is so tough that you can't kill it without spending a considerable amount of time and energy on healing, then maybe you shouldn't be attacking the rogue. Instead, you should attack things at the level of your character and let the stronger character attack the stronger mobs.
There is a problem with this which I refered to in my previous post. With enough pots and 2 /10 weapons an inexperienced fighter can fight outside his weight class. Why should it, theoretically, be different for mages?
They're going to remove the ability to drink large amounts of potions during a battle, and casting a spell leaves you vulnerable. Casting a healing spell on yourself while someone is trying to kill you with a big sword or axe
should create a problem for you. You're basically running away from the mob. And IMO, if you run away from it, then it's fair game for everyone else.
Really, healing mages and clerics should be
supporting magic users for a group. It used to be that we would always team up to fight the rogues, ulbernaughts, and briggands. Now, it seems like almost no one fights as part of a group. If you can heal yourself easily during a battle, then that's even less motivation for people to work together.