Having served on a school board for many years I can safely say that an employment contract between a school and one of its employees is, for all intents and purposes, a one way street. If a school reneges on a contract for one of its employees with no legal, moral or ethical basis in fact, that school can, will and should be sued into the stone age. If an employee breaks their contract with the school, I have rarely seen a school that would pay the legal expenses and suffer the negative PR and ill will in the community to enforce the provisions of the contact.
I have no idea the particular circumstances of this situation.
I will say that signing a contract and giving someone your word is the same thing. You have made a commitment. If you say you'll be there, be there.
Like I said, I have no idea the particular circumstances of this situation or any other situation mentioned in this thread. If you have made no commitment (written, verbal, handshake or otherwise) then by all means you should do what is in the best interests of you and your family. If the school has not honored the provisions of their contractual obligation to you, you have every right to do what's best for you. But if you have given someone your word and that's all there is to it, you should honor your word. Period! I've watched a lot of teachers, coaches, administrators and employees leave their schools in a lurch at the 11th hour because something better came along and justify it by saying they simply had to "do what was best for them and their family". I don't buy it, agree with it or condone it.