Was there even a mass exodus? I largely avoid Reddit now, but I do kind of doubt that they've been hurt in any meaningful way by all the protests and people leaving...
I have to wonder how much of Reddit's traffic is bots and lurkers though.
Post quality is a bigger indicator, and that does seem to be dropping. This is why Reddit banning 3rd party apps was such a big deal. It doesn't matter if 99% of your users use the official app if 99% of the content posted to the side is posted by the 1% that don't.
As someone who was around for the digg migration, it didn't drop off overnight (hell digg.com is still around), but they gradually bled content until everyone was on Reddit. Lemmy right now is very reminiscent of early Reddit.