I think the important point here is to make sure the NW/DL management is crystal clear that this is a really dumb idea and it's likely to cost the company a LOT more than it saves/makes.

I am one such case study. I started looking for a second regular carrier because I got tired of the decline in both product and service at US. I've been a CP for many years (HP Plat before the merger) and usually clocking over 150K BIS miles annually with them. I also rarely ever buy highly discounted fares because my work travels are often booked late and/or require flexibility.

Got my NW Plat 2 years ago (comped to G and made Plat in a month) and as of July 2008, my total BIS with US is about 20K. Sure there're 5 more months to go but it's not gonna change a whole lot.

I have opted for $900 US tickets over $400 WN tickets because of the in-seat power on some US metals and because I want to stick with my carrier of choice (so long as it's within my budget limits). I also like my upgrades especially the instant Y-ups. Now, US is a third choice after NW and CO. Even post NW/DL merger and the CO alliance changes where we lose some of the benefits, little will change.

Apart from the US nickle & dime actions, the one huge difference between US and NW is how US appears to loath its elites while NW really takes care of its VFFs.

Btw, there are many in my scenario and most of them flat out bolted to other carriers cleanly instead of straddling 2 for a while. All VFFs and mostly higher rev pax.