Actually I have made some progress for future reference of anyone with similar problem.
Thanks to Planet Fedora I picked up this entry today [in French!] >
Anyway, the clue is that by adding the three lines to my /etc/modprobe.conf
file, I was able to boot today with the USB microphone plugged in, without losing my audio output.
alias snd-card-1 snd_usb_audio
options snd-card-1 index=1
options snd_usb_audio index=1
I have to do more checking with other scenarios, such as having it unplugged when booting, to make sure that still works fine. Only glitch today was that the microphone was muted at start.
If anyone has any other suggestions, I'm listening.