Something everyone seems to forget is that White Pass spent quite a bit of money rebuilding these. Big companies often have weird ways of valuing something for resale, sometimes the book value or asking price is dirt cheap and other times outrageously overpriced. Just because you invested too much in something doesn't mean that someone else is necessarily going to pay you enough to recover your investment. The true value of something is what a buyer is willing and able to pay the seller.
When these were rebuilt over several years, rumor has it there were two different microprocessor control systems used. The problem with this is that there have already been several microprocessor control systems orphaned because either the manufacturer went out of business or no longer supports the system. And you don't potentially need just new hardware, but the software which is all customized per locomotive model. Compare this to a 50 year old relay which can usually be easily replaced with a modern common equivalent. When rebuilt, these were given new Cummins "green" engines and traction alternators. This were never intended to have a 25 year life. And ask anyone that has a modern diesel - when anything goes wrong with the emissions system (which is apparently their Achilles heel), they shut down and pout, typically without warning. And these had certain improvements which basically makes them a Frankenstein design, I don't know how well they were re-engineered. Again - rumor mill says White Pass has been less than pleased with them, but if so why did they keep having the rebuilt, especially considering the last unit was salvaged for parts as the rebuilder simply failed and walked away?
What you may have overlooked is that it may actually be the ALCo/MLW units that will be retired first, as they are the oldest without a major rebuild (except the 114 after the wreck repair?).
Then again - 36" gage road diesel-electrics are extremely rare and almost non-existent in North America. If White Pass lets whatever they retire go cheap enough, it might be to D&S and/or CATS advantage to buy some even if they were to sit on them as cores for future use. There might be some competition from a couple places in South America as they seem to be picking up used units and rebuilding them for their own use.