I saw a few KUBs with the warning 'Critical air pressure loss'
and the BC drives on. Don't know if it's a matter of time such an
accident would have happened, but maybe this will be a wake-up
call.
it will only reduce the speed by a bit which will not affect
much. unless the bus is travelling at very slow speed then maybe
changing to neutral will have some effects.
A vehicle will coast when it switched to neutral. Any torque
will not longer be chanelled to the wheel, and the rev will jump up
since the power now goes nowhere.
You're probably worse off in neutral while in motion because you
will no longer have any engine power (be it acceleration or
decceleration) but only the steering wheel.
If the Voith retarder was working as intended, he should be able
to get a little bit of engine braking so long his foot is off the
gas pedal. (Definitely more than if he set the gearbox to
neutral).