Is the guarantor required to pay the amount for which he guaranteed a person who embezzled money, given that the guarantee was conditional upon the employer waiving his claim against the employee, which did not happen?

You are not obligated to repay the money to your employer because he did not fulfill the agreed-upon condition, which was his waiver of the lawsuit against the debtor. Therefore, he has no right to demand payment from you. Imam Al-Shafi'i said: "If the guarantee was conditional, then the creditor has the right to hold the guarantor to what was stipulated for him, not to what was not stipulated for him."