Resigned, then terminated, policy for vaca pay differentiates between vol/invol

In Pennsylvania, an at-will state, a 7-year management employee resigns and provides the required 4-week notice and is immediately terminated. Written formal Policy Manual is in place and states payment will be made for accrued vacation and sick time when voluntary separation occurs, but will NOT be paid when involuntary separation occurs. In this case of resignation with proper notice and then immediate termination, is this employee considered voluntarily separated or involuntarily separated with regard to payment of accrued vacation and sick benefits based on the written Policy Manual? Hundreds of vaca/sick hours have been accrued. Employer refused to pay. Might a Wage Complaint filing with the PA DOL (PA Wage Payment and Collection Law) be successful? Or is the employer's involuntary termination of the employee a clever way to avoid paying accrued earned vacation and sick hours? See policy excerpt below.
RESIGNATIONS
Employees who wish to resign are required to give the department manager ten (10) business days/two (2) weeks written notice. Management and professional staff are required to give four (4) weeks notice.
TERMINATION PAY
Employees voluntarily terminating their employment with proper notice will receive a final paycheck on the next regular payday. Their final check will include payment for all hours worked in the pay period, earned but unused Vacation days (if termination is 91 days after the Date of Hire) less any pre-authorized deductions and one-half of any unused Sick/Personal Time.
An employee who voluntarily terminates with the required 10 business days’ notice (if termination is 91 days after the Date of Hire) will be paid for his/her unused Vacation and 50% of unused Sick/Personal Time in the final paycheck. An employee who is involuntarily terminated or who voluntarily terminates without providing the required 10 business days’ notice will not be paid for his/her unused Vacation or Sick/Personal Time.
An employee who is involuntarily terminated as a result of a business decision such as a layoff, downsizing or restructuring will be treated as an employee who voluntarily terminated with the proper notice. At the end of employment, Vacation allotment will be calculated based upon the last day of employment. If the employee has taken more time than allotted, the employee’s final pay will be reduced by that amount.