Right now when a player disconnects while inside a Gamemode arena, we kill their sleeping body, but with your suggestion, it wouldn't make a difference because either way their inventory gets reset when entering or leaving arenas/lobby and stays locked, so there's no advantage to keeping their bodies, it's actually better to clean them up even if they're unnetworked/invisible
What you're suggesting would make more sense if we allowed players to keep their inventory from normal gameplay when joining the lobby, which is something I actually plan to add in an upcoming update