Prevent submission of request if there is a break in employee line manager hierarchy

Issue: Employees submitting requests (e.g. Annual Leave request) but if there is a break in line manager hierarchy, request falls over. Appreciate this is correct behaviour.
Monitoring and updating of employee records to ensure that line manager field is populated with active member of staff - but sometimes occurs only after fallen over request.

Question: Seeking solution that will prevent attempted request kicking off the workflow that would then fall over if line manager hierarchy broken.

Scenario: I'm an employee with a broken line manager hierarchy. I attempt to submit annual leave request. Prevented from submit completing, and presented with a warning message.