Unless you can find a WiFi card where the firmware is in ROM, it’s an academic question.
Purism doesn’t manufacture WiFi cards, therefore is limited by what the market provides. I am not aware of any current technology WiFi cards where the firmware is in ROM - but if you can find one, then you can swap it out and nothing about the software side of things will prevent you using that card or prevent you running a FSF-endorsed distro.
In other words, “firmware in a file” is not the problem. The WiFi card is the problem (for needing the firmware in the first place).
Unfortunately the Librem 11 is the wrong platform to be contemplating this because it doesn’t appear to be designed to make it easy or even possible(?) to swap out the WiFi card c.f. Librem 5 or Librem 14.