Ragnarok Proofing: Played straight. Apart from being better built in the first place (after all, when you can expect to live for something on the far side of a thousand years, you don’t go around building houses that will only last mere decades or centuries – and much the same goes for other durable goods – but these days, much of the infrastructure is automated and most things come with extensive self-repair and mutual-repair systems. If everyone left or dropped dead tomorrow, sure, things wouldn’t be perfect, but the material side of Imperial civilization would still be in astonishingly good repair thousands of years, maybe even tens of thousands of years or more, later. (Leaving aside, for this example, the Civilization-Backup Ships and any automated-emergency mind-state instantiations running on Proceed Unless Cancelled, Else Iterate orders.)
Also, of course, bloody dangerous. The automated defense systems are included in that automated/self-repairing paradigm. It might not be in such good shape, it is fair to say, after you’ve fought your way in to look at it and subdued the local autoconstabulary.