That's the joy of owning old aircraft as opposed to leasing new ones - how much does a grounded 737 cost, if you own it completely? Obviously something, but it doesn't just bleed money for you at least. It's just not making money. Plus, from what I'm told at least, most flights are quite full (70%-100%). Even with a reduced schedule, the aircraft that are flying have good utilisation figures, so how does that affect things? It's only the -500's which are on a lease-buy arrangement, and they're flying reasonably well. The 767 is leased, but I have no idea of the loads.
Anyway, if things were to pick up even slightly, Nationwide would start to encounter crewing problems (again). Good news for the F/O's, as has been said.