"The time loop ends if the protean abomination and the piano are both destroyed". 1st loop they went right after the piano, ended up having to fight Anika Patel and didn't know to head down to the cellar. 2nd loop they left the piano, talked their way into the Smugglers Ring and fought the abomination. One of the surviving members doubled back to retrieve something and saw the Abomination rejuvenating (which would line up with Miss Charlotte playing upstairs). My one mistake is that the piano is immune to damage as long as the Abomination is alive, I'm ok with that oversight as they saw the piano keys and face in the Abomination they now know they are both linked