BrainModular

Occasionally, one of the VSTi's I use has a massive failure and creates an explosion of white noise (very startling when wearing headphones!)

Clearly, one doesn't want this to happen during a live performance, so is there some way of killing the audio if it goes above a certain threshold?

you can make a system that check the peaks using peaklimiter in analysis, if there is a peak it affect 0 to the volume out of your vsti,
using ie a 'pass'.

use a limiter Use the limiter patch ?
or the draw compressor where you can draw the compression curve as you want.
All are in the library.