If an employee is absent due to vacation or personal problem then the project will be delayed if no planning was made prior to the employee leave. The project manager should get a head notice before the employee has to leave so they would have time to change the schedule. Communication is key for the schedule to be intact and so there wouldn’t be major problems for the project. If the schedule cannot be change then other members should be recuited to take over the task. This would help keep the project running as scheduled.