Where could he possibly go with it? Do y'all really think there is some god of death in the one piece world?
Tbh, while I'm not 100% confident Oda would introduce something like this, I'm not sure why it sounds so ridiculous to some people considering the kind of universe One Piece is.
People get super-powers from eating mysterious fruits from the bottom of the ocean. Zoro manifests extra heads and arms with no explanation. Sanji creates flames from having "passion," lol.
Either way, I'm not even saying there will be a real journey to the underworld or something. It could be a spiritual journey inside Zoro's mind. But like....why draw a literal Shinigami and have it completely off-screened with no explanation for like 4 chapters if it's just gonna end up being brushed off as nothing?
I still think all of this will lead into lore about either the Shimotsuki or black blades. Wano is supposed to be ending really damn soon and we've still gotten nothing about those things.