Certainly this is all speculative, and I hope things don't get to the point where parking the M80's is the only option. However the airline industry news is growing increasinly dire, and one wonders what belt-tightening might become necessary.
The M80's are definitely less fuel efficient than more modern aircraft, although Midwest's costs are perhaps not as reputed to be. These are stats for M80's in the 12 months ended September 2007. I believe they came from Aviation Daily
Carrier.....Stage Length....M80 cost per ASM
Delta.............588mi...........7.5 cents
Alaska...........899mi...........7.1 cents
American........876mi...........7.0 cents
Midwest......1,210mi...........5.2 cents
Allegiant........945mi...........5.1 cents
Certainly Midwest's longer stage lengths help push Midwest's CASM down, and fuel is higher now than in that period. However Midwest's M80 costs are not as bloated as conventional wisdom might hold.
Yet it's not a shock that the higher fuel burn difference is magnified as fuel gets more costly. Among other advantages of the TPG/NWA deal was the possibility to get fuel and insurnace at lower rates than Midwest alone could get. That may help keep the M80 in the air. And as Blue mentioned, Midwest benefitted from successful fuel hedge programs in recent years, and this *may* help keep the M80 a viable aircraft in the near term as well.
The possibility of either acquring some used 737 or A320 based on a looming glut of parked aircraft is interesting. This is where the availability of internal capital (TPG) may be key. (Thought at first blush somewhat appealing at the time, I hate to think what condition Midwest would be in now had they found a way to take the company private with a hyper-leveraged buyout.) As for the possibility of NW doing MKE-west coast flying as YX*, I suppose it is possible as a stopgap measure. From a PR perspective they'd be better doing a wet lease (aircraft and crew) from anybody *except* NW as it would lead to further belief that NW has taken over YX.
As I've stated before, I do hope that it does not become necessary to park the M80's, not until Midwest has aircraft to replace them. But with so many other airlines showing severe signs of fuel stress, I wonder what Midwest faces.