I think UAL/U will eventually merge, UAL being the name kept.
The others are tricky it could be..
/DL and AA
/NWA with AA
remaining as the third and fourth carriers.
One thing I do know..
will not merge with each other, meaning those three would have to merge with one of the other three..
, NWA, U.
SO my prediction is..
and either DL
with NWA or AA