Man, I don't know. I know this is just a personal anecdote, but around my friend circle, I haven't gotten a single share from reddit in over a month when we used to send links back and forth daily. Those same people have said they haven't visited reddit in a month, other than the rare checkin on the drama.
I'm sure the significance of the impact is relatively small, but I'd also guess many of those that left were heavy users and contributors. I'll go over there to check every few days and have noticed the content quality is significantly worse than 2 months ago.
That said, it is also very possible this whole thing blows over and the million or so of us that left are meaningless in reddits overall lifespan.
Let's call this what it actually was though, there was no attempt at making money from the API. This was entirely to shut down 3rd party apps. Smart AI companies will just scrape reddit. The only people affected by this are 3rd party app developers and users.
This is even more amazingly incompetent. There are a near infinite other ways they could have handled 3rd party apps not showing ads, but they instead chose the brute force method that makes no one happy.
Reddit is incompetence. That is their lifeblood.