Okay I've come up with 3 off the top of my head...
1. A written contract that would be binding on a successor
2. Only be subject to discipline for "just cause" - With an appeal path all the way to the Supreme Court.
3. Right to force the company to negotiate with you in "good faith" or face self-help.
You mentioned Com Air, Mesa, and ASA
Mesa - work rules/pay sucks, but they ended up utilizing a LOT of negotiating capital getting a solid scope and all of the MAG pilot-groups under one contract. They will have much more leverage the next time. Pilots only bitch about pay rates/work rules, but there is a reason Scope is Section 1 of every ALPA pilot contract.
ASA - what about them? The way I see it, it is your beloved management that is putting the screws to this pilot group. If your management had it their way, there would be no ASA pilot group...their contract-and the fact they were unionized is the only thing that is keeping your management from ramming your payrates/workrules down their throats.
ComAir - There company went bankrupt, it had nothing to do with ALPA. They spent the last few years with an industry (regional industry) leading contract.
Let me ask you this...
If the Skywest pilots were themselves on the receiving end...
What would stop management from suddenly cutting your pay rates say...UAL cancelled your code-share?
Say Skywest had to furlough, what would stop your management from furloughing for convinience instead of seniority? Let's see, that Midwest deal didn't work out...let's close the Milwaukee base - all Milwaukee pilots are furloughed regardless of seniority. Do you think the rest of your non-furloughed pilots would put up a fight?
If Skywest were bought by another carrier - say Mesa, what would stop Mesa from dissolving your pilot group and giving you a "take it or leave it" proposition. Maybe you will be lucky and they will give you a preferential interview. I'll give you a hint, the answer is a 7 letter word that starts with n and ends in g n_ _ _ _ _ g!
Good luck.