I guess it all depends on how you define when you're "in a corner." When I was punished in grade school, we weren't required to actually touch the line where the walls come together, so being in the vicinity is close enough to use the term in my mind.
I suppose that if you were flying an aircraft that had both a wicked Mach tuck tendency and deplorable stall characteristics, the very tip of the coffin corner situation could be truly harrowing. But as was stated earlier, in order to get to that singular point where you're well and truly screwed, you'd have to make a very deliberate effort at getting there as the critical speeds converge (barring some crazy NF-104 type zoom maneuver that punts you into ballistic territory). Not something you're likely to wander into.
And if either of the two critical cases prove to be controllable, you could either ride the stall or put up with the Mach buffet until you're low enough to have some breathing room again.