Look at their quarterly profits/losses and make a decision.
Southwest and JetBlue made money last quarter.
For the majors, CO lost $30-some million, and NW lost $40-some million.
AA/UA/DL all lost several hundred million $.
So, from a viability perspective, NW probably had the least damage (lowest loss for its size), plus it owns a lot of its (old) aircraft.
Obviously you'll have to make your own decisions, but if I lived in NYC and was in your shoes and wanted a major, I'd leverage the NW/CO partnership and put my miles in NW and fly either NW or CO (using CO's EWR strength for non-stops).