I mean they would just scrape it if there's no data dump. It just makes it harder for the small guys. They probably scraped and are scraping HackerNews.

Generative AI doesn't follow copyright or even explicit software licenses as we have seen in AI art with human signatures and Microsoft Copilot.

There was always the possibility of some sort of aggregator/other front end sitting on top of the SO data. We just didn't know exactly what a successful one would look like until relatively recently. I always limited how much I contributed based on that as likely outcome. Discontinuing the data dump is a much bigger deal to me and completely changes the value proposition of their various sites.

For what it's worth, as someone who has put a lot of writing online, I'm not bothered by having my writing including in the training sets of these LLMs. I write because I want to share knowledge, and it isn't important whether people get the knowledge directly from me versus mediated by friends, LLMs, etc.