They have to give you a job and pay you the days on your contract, they don't have to have you as the band director. Your contract is a teaching contract in the district and only guarantees you can only be put in a classroom you are certified for. Hall duty, lunch duty, para duties, or In-school suspension do not require certifications. That means while they can't stick you in a math classroom they can put you other places.
Once you are no longer a band director you no longer get a stipend. You also must have your principal as a reference for your next job and those "dream" jobs want to see what you are doing at contest so good luck explaining why you have a 1 or 2 year gap in UIL ratings. "Well, I got into over documentation of my superintendent so I was re-assigned to the in school suspension students and didn't get to teach music for the year".....
This is a HORRIBLE idea and would not end well!