As someone who used to fly CO all the time because I lived in Houston, and who suffered with the employees through the Lorenzo years, I fail to see what CO gains from a merger with any of the other Big 5.
CO made a profit in 4th quarter. The rest of us (and especially my airline, AA) lost money. CO is repeatedly favored as the best airline by business travelers. The rest of us are lucky if those same business people don't just spit in our faces.
Granted, there are some routes that CO does not fly, or have the equipment to fly. So? There's a little airline called Southwest that flies to even fewer places and they put all of us to shame in the 4th quarter (and, for most quarters over the past 18 years). It seems to me that CO has learned the lesson that WN evidently knew from the very beginning. Decide what you are good at, and do it. And, don't worry about the things you aren't doing.
As I said in the earlier post, CO gains pretty much every added advantage it needed just by joining the Star Alliance (though, staying with Skyteam would have had the same result in my opinion).
And, by stopping there, they avoid all the myriad problems that come from a merger. (See also, AA/TWA, US/HP, et al). I'm not including the DL/NW merger. It isn't settled enough yet to determine the success or failure, but because of the highly unionized workforce on one side vs. the predominantly non-union workforce on the other, I don't think it's going to be pretty down the road.
Just my $0.02. No, I will not take a check. Cash or valid credit card only.