First off, this merger won't happen. It'll be DL/NW if anything. Much less overlap, fewer job loses and a much stronger overall route structure.
In the unlikely event DL/US was allowed, the resulting carrier would be foolish to sell a shuttle intact. The MAT should be the shuttle facility and LGA gates and slots that have to be sold off should be spread to as many competitors as possible. There is nothing to say there has to be two shuttle operators. They would be short-sighted to take the money now and allow a strong competitor to take root.