If it is true that DH thinks all no voters should leave the union - and I have no knowledge either way - it would be a foolish thing to suggest. BASSA has lost some c2500 members over the last 18 months, another c1500 would seriously diminish the influence that BASSA has, indeed it would push it toward the point where BA may consider de-recognition.
Even if they maintain the recognition there would be significantly less people for BASSA to call upon when they need industrial muscle. This will not be the only dispute that BASSA gets into with BA, telling people to leave the union will leave BASSA much weaker when and if it has a really important problem with BA that genuinely motivates a vast majority of members. I'm not sure that even DH is so stupid as to suggest such a thing.