I was a frequent visitor to Fegua between 1968 and 1980 and during that period saw no evidence of systematic large scale scrapping. Which is not to say it didn't happen, but we didn't see it while traveling over the line and looking at the various roundhouse facilities. From the mid-60's until the "Spanish" diesels arrived around 1972 the best of the out of service steam was being pressed back into service, and presumably the balance was serving as a parts source. What happened after 1968 I can't really say, but clearly engines started disappearing. I wonder what the market for scrap metal was. I would think that Henry Posner could provide some information. Not sure what you meant by how long did the Krupps last. I believe at least one still exists in the Guatemala City museum and was dragged there from Zacapa in the last mainline move over the rallroad before Henry shut it down. Our last charter in 1980 was pulled by a Krupp and they seemed to get about the same shop attention as the Baldwins. Good luck with your hunt.
JBWX