No union can prevent a buyout. The DHL transaction involved Deutschebank which, under foreign ownership rules, required them to spin off the air portion (ABX/Astar). ALPA could not have prevented what happened either. Up until that point, Teamsters negotiated the highest pay scales in the industry for ABX. In the aftermath, Teamsters also managed to secure $75M from DHL for the laid-off pilots. This amounted to a 6-figure settlement for most of them. In similar fashion, NetJets contract was also negotiated by Teamsters and had the highest wages in the fractional sector. I haven't seen similar success stories coming from ALPA in decades; all they've done is allow the industry to be over populated with Barbie jets at the expense of main line jobs.

Unions aren't the cure to all problems and won't prevent macro-level financial decisions or bankruptcies, but as long as you're employed by an unscrupulous (and profitable) management team, you better have one if you hope to have a life. At the end of the day, it's not so much the brand, but the MEC leadership, membership involvement and management cooperation that drives the success.