Sorry to hear about your friend's accident - glad no one got hurt. You have to be a bit patient around this LX forum; it's not the most active area around here, as you can see...
I don't know the "official" answer. However, based on my understanding of how this airbag system works, where either the stitching or the side of the seat cover "break" when deployment occurs, my sense is that the seat cover will need to be replaced in conjunction with the airbag. You can always email Sewell parts or your local parts department to inquire.