Good question.

If the document is dropped by the IETF, nothing at all would happen. It's already a valid code point registration, and indeed the authors could have just published the document, registered the code points, and stopped (see: https://datatracker.ietf.org/doc/draft-barnes-tls-this-could...).

If the authors decided to later pick up the document somewhere else, then they could probably get the reference changed to whatever that was, as long as the semantics were identical.

Thanks for the link to that amazing document!