I reckon Class Halls will be staying, reason is Class Mounts will be obtainable still after Legion. I'm sure that was said on a blue post or an interview posted on MMO-Champ.
As for weapons, I reckon they will be drained - ultimately keeping them around for more nostalgia and placed into the Class Halls because in the end, things like Ashbringer or Doomhammer being destroyed would be like trying to remove the strips of the United States Flags... It's too iconic and in-grained in the Universe to completely abandon them to the echoes of playerbase hear'say.
If you believe we are venturing towards Northrend again like I do, Frostmourne being drained could help with the era of Bolvar as Lich King... And kinda play out with strengths such as deframing you as the Deathlord and reduce you down to a pawn that was played ever so cleverly by Bolvar into doing his bidding like raise four new Horsemen and things from their Class Mounts campaign - which would work with others. Rather than being in the lead so to speak as you are now, you get knocked back down to above average standards.