I'm not convinced by your argument. I'm not sure what you mean by 'something catastrophic happens'. 'Something catastrophic' is the result of a certain chain of events. Telemetry data about those events can be sent before they lead to 'something catastrophic' that makes it impossible to send anything further. It is not as if the plane hits a meteor in mid flight and everything suddenly explodes with no prior indication of anything going wrong. And even if that's the case (as being accidentally hit by a missile during training - this happened before) - the lack of telemetry will also tell us something.
I'm not thinking of meteors when I describe a "catastrophic" event. I'm thinking of a fuel tank explosion like TWA Flight 800 or a missile hitting the plane or a bomb in the cargo hold going off or a stress fracture on the fuselage causing an inflight breakup. None of which have been ruled out on the Malaysian flight, I should add.
Those "catastrophic" events represent a tiny percentage of flight crashes, and a black-box wouldn't help to properly diagnose them either. Your argument still doesn't make sense.
