A lot of it did survive during the Byzantine era and big industrial projects such as harbours and bridges were still being built. People would have kept it and maintained it but the black plague and famine destroyed the population and economy. These ancient megaprojects need a large population to maintain and a lot of money, neither of which was available.
AI programming. I feel like it will get to the point where AI will start writing code that works but nobody can understand or maintain including AI.
If you are able to explain the requirements to an AI so fully that the AI can do it correctly it would have taken shorter time to program by yourself.
AI powered code completion is another story though and I’m looking forward to it.