I was actually thinking of how we'd do that Lord!

The only idea I've come up with is that every single bonfire will have a keeper NPC, wavering in relevance to the actual plot. When we rest at a bonfire, we imprint upon it so that when we are struck down the respective firekeeper to the previous bonfire we rested at is made aware and uses a summoning magic; somewhat similar to using a soapstone, to bring your body back to the fire for her to tend to.

That's just an idea, if anyone has any others I'd really appreciate hearing them cause I'm not completely sold on that one.

EDIT: ofcoarse that doesn't explain how people came back before coming to Lordran and resting at a bonfire but let's not get into that for the sake of convenience.