The most likely outcome for the yucca plant, if the yucca moth goes extinct, is "The yucca plant would also go extinct."
This is because the yucca plant relies on the yucca moth for pollination, and without the moth, it would struggle to reproduce. While there is a possibility for other options like adaptation or human intervention, the dependence is specifically tied between these two species in a mutualistic relationship. If no alternative pollinator can effectively take over the role of the yucca moth, the yucca plant would face significant reproductive challenges and could ultimately go extinct.