He’s constantly being asked about it by the press and is trying to force the owners hand to try and get him to release some funds. What makes you think he hasn’t spoken to the board? We don’t know what’s gone on behind the scenes. Given how candid he is with the press I’d be surprised if he hasn’t.
It’s up to him whether he walks, he’s under no obligation too. The fans love him, and largely hate Ashley so the board have to be careful since they’re actively trying to sell the club. If he walks, they’ll odds on to go down with no guarantee of bouncing back and then Ashley is either lumbered with the club or selling at less than the £350 million he’s after now.
If the board are refusing to back him, and he thinks the money he's getting isn't enough to stay in the league, even moaning in the press isn't yielding result, why should he stay ?