My engineering head says that most of the time the current pitot probes work well enough, and it is an extremely rare occurrence that all three are lost with such tragic consequences.
There is in my mind, one obvious emergency alternative, that is already fitted to these planes, the ram air turbine.
I would imagine that a simple emergency system that was able to deduce the air speed from the RAT output could provide a viable emergency backup airspeed indication, albeit probably less accurate and no so efficient. Mind you if you have nothing else, an inefficient and not quite so accurate method of measuring your airspeed would no doubt still be very welcome.