I had the same problem, I just lost my star DM and I had plenty of cash but wasn't able to offer him more than 7k pw due to board restrictions! He was on holiday in the offseason so I couldn't talk to him him either. His happiness was almost maxed in the coach report screen, I'm listed in his favored personnel plus he was my captain!
Good luck, but I think once a player makes his mind up its pretty much done. I'm just making sure I do a check of all my players contracts twice a year now so that I can try to re-sign the ones I want to keep early.