The ratio of users that I remember Redditors often passed around was ten percent of users were active contributors that created new content and were active everywhere in all the subs. Every sub has a core group of people that create most of the content and drive conversations and connections. The rest of the 90 percent are lurking in the background and most just read and watch, several may take part and generally just repeat and repost content that was already created by someone else.

Once enough of those core dedicated Redditors leave, it will severely affect content. But even so, there is so much content on the site already that users can just repost old stuff endlessly and still drive traffic .... hell they could even just get the bots to just regularly bring up old popular content that users would see as new.

If Reddit does change for the worse, it will take time and it won't happen fast .... it will take months but probably a year or two to see any significant change.