I don't think anyone other than Kean is in danger right now, not even Martinez. Managers like Wenger, Mancini, and Bruce will be backed by their boards to see out the season before wielding the axe, I would think. Wenger because he still has their respect despite their poor start to the season, Mancini because he ended a 35 year wait for the FA Cup, and Bruce because they actually like him.
The only other manager who would be in trouble come end of the season would be Daglish should he fail to deliver top 4 - FSG are results oriented and they've set the standard for this season because they know that it is the foundation upon which the seasons that follow are built. Say what you like about spending 110m pounds, I don't think that is more important to FSG than having the man miss their target. If he scoops a cup along the way though it's harder to call...