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.