I bet if someone else offered to double your salary to do the same job, you'd leave too. Don't kid yourself.
Um, no, not if I had a contract. Generally, breaking a contract has serious financial repercussions... as it should. Two-year contracts with daunting out clauses should be standard for a new coach in a rebuilding program. Otherwise, you'll see just what you're seeing now-- opportunists with no loyalty jumping ship before they've completed what they were hired to do.
Don't kid yourself-- breaking a contract should be economically painful, not rewarding. Otherwise, why bother?