Many of those details are negotiated as part of the merger with several parties involved, but they are going to be folded into the seniority list based on hire dates. I've never witnessed a case where every employee of one airline was tacked on to the bottom of the list of the other.
By the way, the only reason Delta would want JB is to throw sand in the face of SW, we have a time honored tradition of doing that to one another. Quite frankly, JB would be the perfect move for SW right now. Diversify the fleet, get the Bus drivers already in tact and trained, and not be so susceptible to the groundings of one type. Plus, that 321 neo has some long legs. She's a dandy! Even if you don't have the neo's yet, it's still the same type rating and their would be plenty of cash on hand to buy some if you merged with us, because SW is very cash heavy.
Don't you have a 1st class? We lose a lot of coach customer's because on other airlines, their is a chance you can upgrade to 1st if their is room and one is assertive about it. We can't offer that, and I personally sometimes fly our competitors for that exact opportunity.