Two candidates, Pete Carroll and our own Mike McCarthy.
Pete Carroll is the Occam's razor candidate - he is a notorious front runner, and he sees the strength of his team is deteriorating before his eyes and he doesn't want to be around when it implodes.
McCarthy makes sense for a couple reasons. One, all season long he has to not only coach the team but also be the public face of the GM as well, while TT hides in a corner avoiding accountability. MM gets paid well for the double duty but in tough seasons it has to burn him out. He's been here for a long time and I can see him wanting a break or a fresh start.
Two, the org structure with contracts is weird right now. TT's contract goes through the 2019 draft, MM's through the 2018 season. That means that TT either gives MM a contract extension after this year which would 1.) be weird coming off a losing season, and 2.) saddle the new GM with an old coach for some number of years, or TT makes him coach through a lame duck season, which you never EVER see with a coach of MM's tenure and pedigree.
If MM does want out after this year then Murphy really needs to move on TT sooner than his contract is up, for the reason mentioned above - would be strange to hire a new coach for 2018 season when you know the GM is leaving after the season and the new GM would presumably want to make his own hire.
It's been all Titletowns and pro-shops for Murphy these past years, but he's going to need to earn his money sooner than later.