The cabin should detach in the event of an emergency. Great plan. It will then need some sort of device to slow its fall to the ground.
Parachutes would be tricky either they are set to open very fast in which case they will rip off and or blend the contents of the cabin at cruising speeds, or they open more slowly in which case they won't have time to save us from a (more likely) accident at low altitudes.
What if we used wings instead? They work over a variety of speeds, especially with deployable high-lift devices, and have the added advantage that they can steer the descending cabin away from pointy death. So there is an emergency, the cabin detatches new wings pop out, along with a some sort of station where someone could sit to control the descent.
That's a very complex system though, there's a lot that could go wrong with all those rarely used mechanisms. Lets just tow a spare plane behind each passanger jet with a rope ladder connecting them.