I went to look for the rules because even though I read the DMG (I'm weird, I also at least skim the manual for new cars too) didn't see any. I saw the rules for random dungeons in Appendix A, but nothing about using them to play a game without a DM.But if there are rules--optional rules, yes, but rules, nonetheless--in the books for playing without a DM, then it's not so impossible as you seem to be claiming.
So I was curious. Are you talking 5E? Am I just missing it?