If their community stays, they will stay. It’s the reason Facebook won’t die either. There are plenty of still good communities on Reddit, so I don’t expect a

If their community stays, they will stay. It’s the reason Facebook won’t die either. There are plenty of still good communities on Reddit, so I don’t expect a Digg-like exodus, which was due to a terrible redesign - you couldn’t even the use the site, so there was almost no choice but to leave. But also there are lots of ways for communities to setup their own decentralized server like Discourse (and some have). You only need a couple of motivated community members. Ultimately Reddit may just devolve into USEnet... flamewars and pornography. But that could take years, and the management will actively try to keep it humming.