I wouldn't read too much into the activities in NYC. The build-up of LGA doesn't mean they're going to ignore the rest of the network. There are plenty of planes and people to go around without killing a hub to make LGA happen.
You are correct, but this is DL. AA did the same thing to STL; there were certainly plenty of planes and people to go around when they acquired TW. AA, however, did indeed kill a hub, mostly to make consolidation at ORD and DFW happen.
The current set of behaviors and decisions by DL management is eerily similar.
MSPers, be prepared to be STL-ized over the next few years. Good luck, you will need it. Maybe you will get lucky and WN will expand greatly at MSP just as they have at STL over the years to fill the domestic void.