This article deals with what might happen after the least likely happens, in only one way of it happening (DL, as opposed to someone else who got what DL would be forced to spin off, getting all of AA's LHR landing slots).

It leaves to the last sentence of the article a much more likely possibility: That AA merges with US rather than with DL. (But there is no big headline about IAG or oneworld then, as US is the minor player in *A, with UA the major player, so US would simply move to OW and then then each of the 3 remaining major networked airlines in the USA would be with one of the 3 alliances.)

Forgetting for a moment the uncertainty of whether DL-AA would ever be really considered, how DL-AA would work (in terms of what DL would get to keep of AA and what it would have to spin off) is not at all clear. If DL couldn't keep any of AA's JFK operations, because DL already has a big JFK presence, then would they get any of AA's JFK-LHR slots??? And if not, wouldn't whoever does have more of a reason to join oneworld???