The 'essential' tag is there so that major quests can be completed without breaking a quest chain. In say, Fallout: New Vegas, all major quest NPCs tended to be located inside, away from wildlife that could kill them, leaving the only way for a quest to fail was for the player to deliberately kill the quest givers. In Skyrim, it could be possible for an important quest NPC to get killed by wildlife, so the essensital status is there for a reason.
It's really only dragons that are a significant threat though - unless you lead a bear into Ivarstead or something, the general wildlife seems not to wander into town. At any rate, it's simple to make sure nothing spawns too close to town. If just dragons were prevented from killing certain NPCs it could work.
Once in New Vegas I imagined the shot in the head had brain damaged my character. I gave them 1 intelligence and 10 strength and endurance and they attacked every single person they met, starting with doc Mitchell. It was fun to go totally berzerk and break the game. Quest fail alerts were popping up all over the place. It was a lot of fun to do that just for a change. You can't go berzerk like that in Skyrim because of the sheer volume of people it's just impossible to kill.