I don't know. He has a point. If you're going to reload anyway if they die, why NOT make them immortal? Basically, you have to make the decision that you're okay with a companion dying to let them stay dead. Otherwise, if you like the companion, you're just going to reload - especially if that death was out of nowhere or stupid. (I.e. your grenade bounced back under their feet, etc.) Having companions not die is no more immersion breaking than reloading all the time.
And I've been reloading for companion deaths since FO1. Ian shoots Dogmeat to death in the back with a SMG? Reload. Dogmeat rushes a Super Mutant? Reload. Dogmeat keeps rushing into damn laser doors in the Master's base?!! Reload. Reload. Reload! Relooooaaaadddd!!! "Dammit, Dogmeat!!"
This can be handled well if they don't just treat your companion like an essential NPC like in past games. If they just ragdoll unconcious and get up afterwards ... yes, that's stupid. But if they go down until combat is over, have a wounded animation, and inform you they need to go back to base to rest up and they'll meet back up with you later .... that could be awesome. You wouldn't have to worry about losing them permanently, but you might get deprived of them for the remainder of a quest until you went back to pick them up again.