TIL not only that alsamixer supports hotplugging, but also that it quotes poetry if the device it’s currently pointing to goes away.
Nice surprises like this make me feel better after all the sound-system wrestling I detailed earlier.
(Also, mumble has been added to the audio-application mix. Thankfully it’s willing to do its output via PulseAudio while it does its input via direct ALSA, so I can use a USB mic with it, which is the only type I currently possess. Three guesses how I discovered the previous statement about alsamixer.)