Unfortunately they probably have some ethics clause loophole that they can exploit to avoid paying him.
Hopefully he has a great lawyer who can say those emails were from 10 years ago and they were private...
He resigned.
I’m certain he has an iron clad contract. If not he wouldn’t have resigned. He would have forced them to fire him. The resignation probably was for the avoidance of a long & expensive court case that the Raiders would have ended up losing.