Why are the lease costs so expensive in the first place?
My guess would be that the trains were procured in roughly 2007/2008, and that Macquarie funded them by lending money on the commercial market. At the time the interest rates on loans were very high (the
BofE lists the April 2008 Bank Rate at 5.00%) and I would expect the interest rate agreed to by Macquarie to be pretty high as well. This has a direct effect on the lease rate.
Whether the loans can be restructured will probably depend on the terms of the original loan, contractual stipulations, and whether Macquarie/Akiem are even willing to go through the hassle.
Interest rates plummeted a few years later (among others due to years of quantitative easing policies) which made buying new, like Greater Anglia have done, much more interesting than continuing the lease of the 379s. Interest rates are rising again, so perhaps eventually the fleet will be of interest again to an operator looking for AC trains.
I wonder how much longer they're willing to keep the 379s around before they decide to have the units scrapped. After all, now they only cost money in upkeep in storage and they have no income from them.