I haven't found a mod that addresses this yet, but I may have overlooked one.

Most of my play throughs have been without followers, but my current game uses UFO with two followers and I'm finding it adds some interesting tactics, particularly for spell casting. However, essential followers can remove some of the challenge. On the other hand, simply making followers mortal allows them to die to silly things like traps and getting stuck behind a rock (making them not very useful past a certain level). I think a middle ground could be found if followers were incapacitated longer when the reach low health - maybe for a minute or maybe until combat ends. This would make healing others, debuffing enemies, or avoiding hitting your companions part of the combat tactics, making them more interesting.

Is this as simple as changing a number in the CK? Or are there mods out there that do it already?