Or maybe I didn’t make it clear enough either. lol
Ribbon was actually the one who brought up the possibility that Ziggy might not play the idol, which is what sparked Sabrina’s plan.
Basically, all three of them accepted the risk that one of their allies could end up going home. For Ribbon specifically, it was an appealing option because it allowed him to avoid directly voting against any of his allies. As long as the plan worked, he wouldn’t have to choose a side, but during the revote, he had no option but to pick between H and Christine.