It could be mounted externally, separate from other systems, and it would be fairly trivial to implement a strictly mechanical means of activating it from inside the vessel. All that would be needed is to open the valve on the external pressure vessel.

If you're referring to getting out once you're on the surface...hell of a lot easier for rescue crews to find you and do that if you've got a huge orange inflatable holding you at the surface, rather than however many thousands of feet underwater.