The other thought I had was who owns the licence to the game system?
The IP goes back to Games Workshop. Does the games that FF made now go to GW too?
Ie can FF make another game reskinned to use the exact same system as WHQTACG and be compatible e.g., with Descent quests and characters and it is fully compatible? Then you could mix characters/quests from WHQTACG. Maybe they could release Descent: The Adventure Card Game and it's exactly the same except with Descent quests and characters? Or any other game they have licence to. They might need to change the name of some of the mechanics or icons on the cards depending on if they hold a licence to those names/icons or not but otherwise it's the same.
OR does the licence to the game system go to GW. In which case since it's already a well designed game it would make sense to just continue with new expansions, reprint the game and existing expansions but with the GW logo instead of the FF logo
I don't know the details of IP laws, but as far as I know, the game's system and mechanics can't be copyrighted. So FFG would only possess the IP from the rulebook and the stories of the different scenarios in the campaign. However, it is considered bad business to completely "steal" another company's game and change the universe, theme and rules to avoid IP lawsuits.
In my opinion, the most likely scenario would be that FFG made a retheme of the game under another universe, like Runebound/Descent.