I feel like most will just stay but it will never feel the same. As for what could possibly replace it, at least for me, it has been a conglomoration of different things serving different purposes. Lemmy is good for seeing discussion, RSS for my own personal link aggregation, and then the occasional browsing of something like Mastodon which just hits a bit different personally. Those together have more or less quenched my desire for reddit for anything except hitting it on Google Search results.
Nothing will ever feel the same. It's an illusion to think that one platform will ever 'replace' another. In my 20+ years of being online (oh God), that has never happened. Platforms will eventually fade away or become unbearable, but the void will be filled by many other niche platforms.
Google+ didn't succeed because it aimed to replace Facebook. Now it's WhatsApp, Telegram, Signal, it's BeReal, it's Instagram, it's TikTok. My guess is that it will be Lemmy for the nerds, Reddit for what "they" think it's for (when I look at "new" Reddit — something like 9gag), and other platforms for what I can't think of yet.
However, the Fediverse certainly reminds me of the internet as it was about 15 years ago when it focused on open protocols and similar aspects. XMPP comes to mind. I am filled with joy when experiencing the freedom and prospect of an Internet without dependency on but commercial companies again.
I actually use my Nextcloud instance's News addon plus Nextnews on iOS so sorry I can't be of more assistance :( Sounds like there are some others in the comments who do though!
Not op but I use feedly and it is pretty good. I think I've used it since right after Google reader went dark so I don't know if there is a better app out there now.
Not OP either but in case you used to enjoy greader as much as I did back in the day, Inoreader feels extremely close.
On the open source side of things, Feeder looks great as well, although I haven't used it myself.