The thing is, 'reddit-likes' have definitively a place in the Internet, and I mean for the next couple decades. This format has been iterated over and over, starting with slashdot, 4chan, digg et al, and it's obviously one of the best ways we ever found to manage large discussions/news/etc. HN is an example.

Reddit is growing and would continue to grow really quickly. There's no competition in sight. Owning the discussion backbone of the internet is massively valuable, comparable at least to WhatsApp I'd say.

Can it die out due to massive exodus? Sure, but something similar will replace it. And for each iteration (slashdot,digg,etc), those websites have become larger and more consolidated. It's fair to assume at some point it will reach long term stability (particularly if it's properly managed).