I'm sure many will go back to Reddit but some wont. I for one will be staying on Lemmy as I've found it a breath of fresh air.

I'm not sure how many users will actually stay away. But if even a small fraction of the mods for these big subs stay away Reddit's gonna have a problem.

Lemmy will pull some mods away, traditional forums will pull some away, and that could really hurt.

However, only time will tell if that ends up happening.

Reddit is already due for a problem regardless of what the mods decide to do. Bots are no longer going to be a thing thus multiplying the work required for a mod by an unknown factor
Wait, can you explain this a bit more? I'm not the most tech savvy, but I'm reading this as things like automod and gandolf bot all being gone - the former being potentially worse? (No hate to LOTR fans, of course!)

Most mod tools and bots rely on API access and are just as affected by this change as third-party Reddit clients.

After the outrage started, Reddit has stated that they will make exceptions for mod tools and accessibility apps, but it requires manual approval, and a number are likely to be declined in spite of it. Particularly when considering that a lot of moderators made use of mod tools which were contained within these third-party clients that are shutting down, and are likely not going to be spun off into separate tools.