We don’t use scrum as such, but we still face the issue of team-member absence during fixed iterations. It’s a tricky one to deal with, especially as absence comes in both predictable and unpredictable forms.
InfoQ has a nice summary of some of these issues and some solutions. There is till no “silver bullet” for this, though. Losing staff will almost always mean losing productivity, which in turn means that iteration (“sprint”) commitments will need to be renegotiated, which works best if stakeholders are informed as soon as possible.