One of our developers has gone on holiday with some tickets associated with them on the Kanban board.
We were faced with the following two options:
Keep the work in progress limit the same for that team, and keep those tickets on the board, but not have them move until the developer returns.
Park the tickets off the board, and reduce the work in progress limit for the duration of their holiday.
In the end we determined which tickets were needed by the respective project and reassigned some other tickets in that team's column. The decision above forced us into having those priority discussions, but I am interested in hearing how others deal with this kind of issue.