No, having to use a stimpack on them to revive them sounds fair. I was watching gopher's lets play of fallout new vegas (he actually opposes companion immortality, so this works as a good example) and whenever he would go into a dungeon he would leave his followers outside. That kind of seems to defeat the purpose of companions imo. If there is content tied to the companion then i think for 90% of people their death is a reload state. As far as a hardcoe mode (i hate that they called it that, survival mode would have been a much more elitism inspiring name) i liked all the changes except for the companion death. It basically ruins any melee follower as they'll be slaughtered by enemies using guns or deathclaws.
Now if people want to dl a mod that removes the essential tag thats their business. Although i don't think that it should be part of the core experience.