Wn would buy them to kill them off , not to merge. Before Rjet bought F9 they were generating about 1 billion in revenue a year . Southwest offered 113 million on there bid. now Wn could offer 80 million and rjet just might bit.Anything could happen, but buying F9 would add a third and maybe 4th fleet type for WN with the potential 4th being Express-type feed by Republic with planes up to the E190. That's a big change to WN's business model and would drive up WN's costs when it's advantage over the network carriers is already shrinking. It would really add significantly to gates at one airport - DEN - where WN has enough gates for it's operation to expand and UA already has a much bigger operation than such a merger would create. F9 is reducing MKE to a spoke airport due at least partially to WN/FL, retreating to it's "home" airport as it's only real hub. F9, 2-3 years after exiting bankruptcy, is still struggling to be profitable (which is why Republic agreed to spin them off in the first place). Then there's the integration mess - Republic has single seniority lists for at least pilots. Would WN employees be happy integrating express employees into the WN lists?
Then there's that route map. Lay a WN/AT route map on top of it and see how many of the same cities are already served by WN/FL. The most successful mergers are when the sum of the two parts is much greater than either individual part. DL/NW combined DL's strong trans-Atlantic network with NW's strong trans-Pacific network. UA/CO did the same. Even US/HP combined a mostly western U.S. carrier with a mostly eastern U.S. and the combined company has been decently successful despite the integration issues.
Jim