A specific chunk of people would for sure move over to Lemmy, and there would be a lot of angry uses, but just because people get angry doesn’t mean they’ll move over. They’ll whine about it but in the end they’ll stay on Reddit.
Personal experience, I tried to move over to Lemmy but when I’m searching for something specific I’ll still look at reddit a lot of the time, just because of the sheer mass of material there is. But I refuse to post on reddit anymore since I don’t want to contribute to it. I’m trying to post more on Lemmy now though, because “be the change you want to see” etc etc.
I know I’m still giving reddit views, which ultimately adds to their revenue through ads. I’m not happy about that. But if I’m having a computer problem, or want to find out why my peace lily plant is dying, I can pretty much always find the answer on reddit. Lemmy isn’t there yet. (Not even close tbh.)
But for the things that are on Lemmy, the quality of discussion is much higher. 99% of reddit comments on the bigger subs are jokes. Funny ones maybe, but not provocative or though-inducing.
tl;dr a lot of people would talk about migrating but it’d blow over and only a minority would follow through.
There’s a big difference between the default subs and the niche subs. There’s bots all over the default subs, especially the news/politics ones. But like, the stardew valley memes sub, for example? I don’t think there’s a whole lot of russian bot activity going on there.