While the advert apparently shows a blatant disregard by Unite for the fate of their own members by clearly linking the dispute, it doesn't change much IMHO.
In my view, the only realistic way Unite could say that any further action is unrelated to the current dispute would be to accept the current BA offer, thus ending this dispute first.
If BASSA are determined to go on strike to exact revenge for ST and the "hostages" without any prior settlement of the existing dispute, they face a serious risk of losing their jobs in an unprotected strike.
BASSA/Unite should give proper, sensible advice to their members of the risks of prolonging this dispute, and they should do it now. They might start by providing their members with the advice given to the leadership from their QC rather than attempt to deflect the blame to BA for the latest ballot fiasco.
If BASSA are so convinced that BA is a bullying employer, then giving that employer an opportunity to dismiss their members is reckless in the extreme.