[ Perhaps in kinder times, Zhongli would find a way to come to a logical conclusion of mercy for Mr. Tibbs. Unfortunately, once death and suffering of civilians is tossed into the mix, he becomes quite less generous. ]

He is an intelligent creature who made his choices and now must face the consequences of his actions.

Unless some new information reveals why he should be spared, I see no reason to offer him the mercy he denied so many. Seal him away or leave him here when you are finished if you are opposed to killing him outright, but fostering further resentment within him will only put others at risk in the future.