Transponder/TCAS failure warning . . .
And what to do when your tpx/tcas goes on vacation en route? It's not a situation where you'd be landing at the nearest suitable airport, nor vacate your RVSM airspace without talking to somebody. A "warning" annunciation of a tpx/tcas failure in flight wouldn't have been a cause for the Legacy crew to have changed route or altitude on their own. One option in case of known system failure would be to offset cruise flight level by 150 feet.