If the liver is not making the urea cycle , then bun should increase ?

Decreases: Urea actually decreases when the liver fails. There are a few inborn errors of metabolism in which you see this. For ordinary folks, by the time this happens, the patient is obvious sick with serious liver failure and monitoring the BUN / urea levels is basically a meaningless exercise.

Will decrease: The urea cycle makes the urea. The "bun" measures urea. Drop in the BUN occurs in liver failure as long as the kidneys are okay, but once this is happening, the fact that the liver is failing is already obvious.