Just for info (from an outsider) but I am pretty sure Air UK Leisure pilots were able to keep their seniority when they were taken over by Air 2000 (First Choice) some years ago.
The argument from BALPA was that Leisure didn't go bust - they were bought out - so why should pilots (who had no control over it) have their careers severely affected by it? Wasn't such good news for Air 2000 crews but that was the downside of their management buying a solvent company.
It all sounds very similar.
PS.
Jim French is probably aware of this as he was, in a previous life, employed by Air UK.