Digg didn't die all at once. It was a very slow, miserable death.
And even now, Digg still exists, with some users even. As long as the Threadiverse gets better and Reddit gets worse, we'll see continued waves of people leaving.
The real question is whether it'll look like Digg -> Reddit (where most everyone left eventually) or Twitter -> Mastodon (where large groups of people were "too confused" and didn't move).