I'll miss the meta subreddits like lostredditors, switcheroo, SubredditSimulator and SubSimulatorGPT2. I'll miss niche communities built around less mainstream games and shows. I'm really going to miss DaystromInstitute and SonicShowerThoughts.
Overall my biggest concern is over the giant stockpile of years of community answers to all kinds of questions. If Reddit falls what happens to all of that? How do we pick up the slack if it does?
I don't see enough people leaving reddit that they have to completely shut down. Most people won't care enough about the changes to leave. The only real threat to old community answers is people who are using tools to delete all of their posts and comments, but even that won't be too widespread