Has anyone tried this? (pendant/bonfire idea)

Sorry if this has been done before, I looked for two minutes and didn't find anything.

what if you were to complete the game (pendant in hand), kill Gwyn and walk away without a single bonfire lit?

To my knowledge it is possible. Simply allow Lautrec to kill Anastacia(?), the firelink shrine keeper. Kill the other firekeepers and don't light any others. It'd be tough for obvious reasons but worth a try.

has anyone attempted/completed this?

yes, I was part of a crew trying the no bonnie runs, fireLESS and Rynn were with me. We tried all sorts of possibilities of a fireless run and came up short. Rynn did have a couple of strange occurrences during an accidental lighting once AND she found a pendant in the empty chest after the gwyndolin fight during a no bonnie run. We were trying to decimate the eternal dragon in ash lake too and that's the only thing that kept our runs from being truly fireless.

cool, i didn't remember the eternal dragon having a bonfire. Finding a pendant in that chest is super weird though