At the moment there is a steady stream of diesels from the 1st to 2nd generation era getting scrapped supplying parts to keep our preserved diesel fleets going, but whats going to happen when they have all gone? I suppose then the worst of the preserved locos are going to be canablized to supply parts, and with pikeys stealing parts whenever anybodies backs are turned only exacerbates the situation. I imagine in your 400 years time scenario, providing we are still civilized I think the serviving diesels will all be museum exibits. Kettles are far easier to keep running indefinitely with fairly rudimentary tools, diesels on the other hand are not.....