MH370 was perfectly capable of sending ACARS traffic by satellite. It just stopped doing so after it vanished. That's why the pings and the telephone call setup messages were the only signals received that way.
As for 'distressed circumstances', you could probably have a very simple system that could be turned on by a satellite message from the ground if contact is lost. It shouldn't have to be any more complex than the systems already used to track shipping containers and trucks.
Of course, it doesn't help if someone pulls the circuit-breaker.