Hi John,
This is a customer specific logic where if the manager is not there then the system must escalate to next level .
As per the standard workflow id it supports only one level of approval and i hope in your case its more than one level so you must have copied the standard workflow id and created a custom one.
Now here you must include a custom logic in workflow that if the work item is not been approved/rejected by the approver for certain period then you can escalate to next level. This can be done by the workflow consultant and at the next level approver can approve through the universal work list in portal.
Hope this solves the query.
Regards,
Mithun k