It's obvious that people would flood Google with generated content. But it's hard to tell if it would kill Google or somehow make Google works better. There's certain dynamics to the game and nobody can say for sure.
As for why it might not make Google worse, just think about YouTube algorithms:
1. One good video is substantially better than hundreds of bad videos, or thousands even.
2. Clickbait works in terms of getting people to click on your video, but if you don't deliver what the clickbait promised people would leave and it would hurt your stats.
3. Generating large amounts of videos may be profitable because it's like collecting peanuts with automation, but that would never reach the mainstream audience like Mr. Beast.
This is because the algorithm promotes videos that are frequently clicked and fully watched. Generated or not, the content must be good enough to be watched through, in order to please the algorithm.
You see, there are a lot of bootleg versions of Stackoverflow, but many of them are terrible. Some of them get ranked because they're still helpful (to the 80% majority of programmers, probably not for the HN elites). We can imagine there would certainly LLM generated versions of those, but very likely with better quality. Generated or not, it's still an arms race to generate more helpful and higher quality content to get traffic.
Also, HN people have been complaining about how the quality of Google degrade over time. It might be Google's fault, but I believe there's another important factor that hurts search engines as a whole - There are too many walled gardens nowadays: Instagram, Discord, and now Twitter, etc. Value information is hiding behind those, which would certainly make search engines less helpful over time.
For example, when I play not very popular video games I wish there are wikis or guides for that. In the old days, I know I can find most of the information in several forums and check the top posts. Now I need to go through Discord and scroll through casual chats and wonder if I missed something.
With LLMs, people would likely be draining that information from walled gardens and compiling them into helpful insights.
Again, there are a lot of dynamics, and it's hard to tell how things would turn out. Maybe it would kill Google and possibly the old Web, maybe it would make the Web great again.