My fix a few years ago for absences was to require any rehearsal missed to be made up with a director or drum major.
I require anyone who missed any portion of rehearsal the week to perform their drill/music on the grid individually for a director the day of the game. This has fixed almost any uneccesaary abscences. Not punishment. It is making sure they are prepared to perform and not endanger anyone else by missing things that could possibly hurt others’ performance.