Hey, you haven't lived til you experience a catastrophic tube failure.
In my experience, you simultaneously get loud crackling and spitting noises from your speakers as a light show appears from the offending amp. This is much better if the lights are dimmed.
Smoke will often rise from the amp's chassis, but with a little luck, the fuse will blow before any serious damage is done.
As you bolt from your easy chair to turn things off, heart racing of course, you'll no doubt get that familiar smell of burnt electrical parts. Gee, it doesn't get any better than that!
Lest anyone think I shy away from tubes on the mere chance one might fail, there are 68 tubes employed between my two systems and I never worry about it.