If a company switches from accrued sick and vacation time to a PTO (combined) benefit, can they wipe out all accrued sick time? Or would that time remain as available sick time if needed? Also, if any employee leaves under the PTO arrangement, befor

If a company switches from accrued sick and vacation time to a PTO (combined) benefit, can they wipe out all accrued sick time? Or would that time remain as available sick time if needed? Also, if any employee leaves under the PTO arrangement, before having taken any time that year, how should vacation time be determined to pay that employee on their last day?