It is sometimes challenging for a project manager to cover the duties and responsibilities who is on vacation or who is having some personal problems. If there are enough funds for the project there could be a temporary replacement for the work. If there is no replacement, then the project manager can seek permission from the upper management to reduce the expectation from the team for some time. All the responsibilities of the employees should be distributed at the beginning of the project. If there is planned vacation of the team members the work can be distributed with other team members. If there is sudden absentees then the project should be delayed or the deadlines should be delayed until the employees return back.