and throwing Y out there won't be disastrous to Y.

The current scenario is so awful that I think there is merit to just bat down the hatches and go with Mangum. He likely gives BYU the best chance to win today and if choice Y is not ready to do better than Mangum is doing it might do more damage to Y than good.

On the other hand these upcoming teams do stink.

I will let the coaches decide, there seems to be little reason to second guess them.