I wasn't active online for the end of MySpace or Digg, but just given their nature and a general idea of how things went, it seems pretty different from reddit. For reddit, there hasn't been a better option come forward, like happened with Facebook. A main component of reddit is the sheer number of users, which means that places like us here or voat will need to really swell in ranks before they offer a real alternative.
Reddit's uniqueness, I think, also means what it's going through is unlikely to happen to Facebook, Tumblr, or Twitter. Those all, like Hubski, rely largely pans direct consumer interaction, through focusing on individuals and rely mainly on sharing on an individual level to 'move' content. Reddit, on the other hand, is grouped up by common interests, and has relatively limited social interaction due to it's voting process. One can vote on a reddit post without commenting, without sharing that you did, and without any interaction with the poster. If we take Hubski for example, since I'm most familiar with it, 'voting' for a post actually shares it (like Facebook or Tumblr), meaning it is visible to your followers and potential followers. When compared to other social media sites, reddit is built in just such a way that a sudden mass exodus is possible, just as a user protest against the administration is also possible.
Also, I doubt it would happen because reddit serves a very different function than Facebook or Twitter. Not only is it anonymous, but it also isn't focused on direct social interaction with real world friends. The focus is so much more on the content, it is, after all, 'the front page of the internet,' that people can leave and find other sources quite easily, while places like Hubski can provide a similar interaction for those who desire that, though generally on a smaller scale.
Finally, I hope the Facebook, Twitter, Tumblr, &c... execs are watching Pap and what is going on for a good idea of what not to do.