While I agree some reduction in flying, and a reduction in a/c would occur subsequent to a merger, I don't see DAL parking all those planes...necessarily.
I'm pretty sure DAL, and all the majors are operating with pretty high pax loads. Maybe that's what your LUV comment was about? Because all the people who fly daily on NWA would have to fly on something. Are those people going to just up and say "oh well, NWA doesn't exist, so I'm going to drive." Probably not. There are also plenty of biz travelers and corporations based in DTW/CVG/MSP who will continue to use whatever int'l departures go out of their city...at pretty much whatever cost. Lots of those Fortune 500 companies have reps whose sole purpose is to lobby for rates and routes out of their hq city. Everyone I know who has Skyteam miles through NWA will follow that carrot wherever it goes, primarily b/c of all the points they have, which would most likely be honored by DAL as an alliance member (if it's NWA, not UAL). Which is another reason NWA is prob a better target than UAl from a marketing/pax loyalty perspective.
If anything, I'd think the potential increase in the post-merger company's oligarchy over flying out of the eastern midwest and southeast would give them a greater ability to pass on fuel costs to pax and better hedge their fuel costs (buy twice as much, you will get a better deal, even if it's a tiny difference). Yeah, LUV could step in and mess with that dominance, but not on international routes, and not on cities they don't fly into/out of.
Does DALs contract prevent them from trying to pull some bs post-merger such as running NWA's DC-9 routes with Compass Embraers and Mesaba 900s??? I'll bet their managment would drool at that idea. That would be something that would screw NWA pilots...would scope stand up from NWA's contract in that situation to protect that from happening???
BTW...this is all 100% hypothetical...no one even knows if anyone is merging with anyone.