You are correct, tournament games cannot be cancelled, only resigned.
Cannot confirm whether or not resigning at this stage will affect your rating.
I recommend simply waiting the 3 days for your opponent to time out.
I can confirm that if your opponent times out any of his games this round, he will be disqualified from all subsequent rounds to help save you from facing this problem too often.
Actually, now I think about it, I’m not so sure. I had an opponent time out by not playing any moves at all just the other day in a tourney and the game was in facf annulled!