What should a manager do when his new boss asks him for a performance review report for the purpose of dismissing underperforming employees, and he fears that he will cause them to lose their livelihoods?

You must do what you have been commanded to do, with truthfulness and honesty, and clarify the truth in evaluating the negligent and the diligent. If someone is dismissed, there is no sin upon you, for Allah alone is the Provider, and no one can cut off sustenance that Allah has decreed for His servant, as He Almighty says: "Whatever mercy Allah grants to people, none can withhold it; and whatever He withholds, none can release it thereafter. And He is the All-Mighty, the All-Wise" [Fatir: 2]. A servant will never be prevented from sustenance that Allah has decreed for him, nor be given sustenance that Allah has not decreed for him, even if all creation were to gather for that purpose, for "the pens have been lifted, and the scrolls have dried."