...Or we could allow players to pick up health potions and store them and allow them to use them at their discretion. To prevent spamming with this system, simply give them a cooldown that makes them more and more inefficient as you use more of them in a given time frame. You could even go a step further and only allow potions to be used in boss areas, thus the normal orb system elsewhere. Then you could choose to only give these potions as quest rewards, which would encourage players to actually experience the plot or perform these side quests you talk about.
Blizzard modifying the Diablo series by eliminating PK, is like Ford modifying the Mustang to look and perform like a minivan.