N903AW,
No big deal, but I think you meant to quote FlyUs.
FlyUs, other than Capital Airlines in '61 I don't know of another UA merger. However when Pan Am went out of business, UA bought their Pacific operation. Pilots were integrated into the seniority list. Since it was before my time, there are certainly others who know more details than me.
Interestingly enough, Delta bought PA's European operation. So a UA/DL merger would actually be a resurrection of the old Pan Am. Maybe they could buy the rights to the name and rename the merged airline. Now there's some food for speculation.