The work force is a dynamic group of people. Staff can enter and leave the organisation, enter and leave teams, and be unavailable for work duties. The natural fluctuations in staff availability should be managed by teams such that there is little to no impact on delivery.
Scrum teams are self-managing.  Whether the word “manager” is in your job title or not, everybody manages something in their work.  Self-managing implies that we strive for teams to decide internally who does what, when and how. Teams should be responsible for their own organisation.
Teams need to manage their own affairs considering such factors as:
People being absent from work is a constant consideration when teams manage their work. Given the roles of Product Owner and Scrum Master perform specific roles within the team, it is important that their responsibilities are carried with people normally performing these roles are absent.
Team members should be explicit in their expectations when the Product Owner or Scrum Master is unavailable. Another member of the team, or a seconded team member should perform these roles where required.
2. Visotcky, R. (2020) The Scrum Team is Self-Managing. https://www.scrum.org/resources/blog/scrum-team-self-managing