Dennis @ PerfectForms
You have two choices:
1)The Notification object allows you to set up an indefinite number of notifications with reminders and escalations. You can use this feature to send escalations to other people in the organization at delayed intervals until the stage has changed: /Documentation/manual/html/?notifications.htm
2)Or you can go in a different direction; Create Positions for your account: /Documentation/manual/html/?d_positions.htm. Create a position for each manager. Assign the position to the workflow role rather than the user license or email address. When a manager goes on vacation, change the person who occupies the position. This allows you to control positions universally rather than on a form-by-form basis.When owners of positions go on vacation they can be easily changed by HR.
3) The best practice would be to use a combination of both methods.