Here is their website
http://www.sabiex.com/
They would be more involved in NATO/French equipments then. Yes they could have survived especially as Braine L'alleud is on the oposite side of Brussel. If Brussel was nuked because of the NATO HQ, this would be quite far away.
About the FN, it has survived except, of course if you chose to nuke Belgium heavily. Moreover, it is more than possible that the entire Meuse valley has survived with its siderurgy, technical industries...
Moreover, coal mines will reopen on the valley providing more ressources to France. All had been closed in the mid-1970's but mostly because exploitation had become too expensive. With the Twilight War this will no longer be an issue.