Wire fan here.
Powell is clearly the man with The Sword of Damocles hanging over his head. He was brought in to shake up the team but nobody, himself included, expected things to go as badly as they did. He's assembled his own squad, he's got max salary cap and training facilities second to non at his disposal. He has to show that he's turned things around within the first 6 games (and he's going to have to do that without McGuire and Dudson) otherwise he'll be out.
McNamara looks to be getting close to the end of his shelf life but I think that he'll make it to the end of the season.
There simply aren't that many quality coaches available so the only way that there will be any mid season depatures is if a club finds itself in such a dire situation that 'things couldn't get any worse'.