are you sure the flight path vector does not require air data?
I can't speak for the manufacturers but mathematically, no it doesn't. The reference platform senses accelerations and integrates them over time to give attitude and position (and from that the flightpath)... Air data not needed.
One way of losing pneumatic input is a birdstrike - often there are several birds involved and they can easily mangle your AoA probes on the way past, so IRU derived data is most likely to be correct at that moment.