Contracts for college basketball coaches are a strange thing. In some sense, they bring security and stability to a program. They can lock a coach in, let returning players know that nothing serious will change, and, with the right coach, entice new players to come somewhere that is in rolling upheaval. On the other hand, they mean essentially nothing if a coach wants to leave. See: literally any coaching change.
On thing an extension does is makes sure that any program trying to poach your coach is going to have to pay. It’s not so much an agreement to stay the length of the extension so much as it is an agreement between both parties to at least leave one another in a mutually advantageous position.