Given that this conference hasn't happened yet, there should still be time for the affected people to report the inappropriate conduct to the organizers and possibly get the paper pulled.
Btw .. I posted a few times on the thread, and want to acknowledge that researchers are humans, and humans do make mistakes. Thankfully in this case, the direct consequence was time wasted, and this is a teaching moment for all involved. In my humble opinion, the researchers should acknowledge in stronger terms they screwed up, do a post-mortem on how this happened, and everyone (including the researchers) should move on with their lives.
https://academia.stackexchange.com/questions/732/why-dont-re.... seems to list out reasons why not to do postmortems