What Hayward did was the real working world equivalent of quitting without notice. He really left us in the worst spot possible because on top of everything his timing made it so we were past prime free agency. He also could have pushed to get us a trade exception, but I'll blame DA for that not happening.
In the end it's not the biggest deal in the world to quit a job without notice, but you are going to burn some bridges and cause some resentment to the people who have to pick up after the chaos you leave behind.