Cheers Chris,
Initially, I was posting thinking that the integrity of the pressure hull had been compromised (but I did have the Ethiopian hijacking in mind at the time of posting). It would seem that with or without an intact fuselage, debris would probable be omitted and make its way to the surface (I don't think 60ft is deep enough to compress seat cushions enough to overcome their natural buoyancy).
A question for those in the know: What does the RAT power? Would deployment of the RAT have initiated the partial, final handshake? It seems to be accepted that the final partial handshake was initiated by the a/c in boot up mode.