Sort of. Digg’s implosion was much more immediate, the changes directly impacted normal users so it was easier to mobilise people, and at the time Reddit was a bit more mature and easier to understand than Lemmy/etc is now.
My guess is we’ll see much more of a Digg-like exodus once Apollo stops working and the average user sees an impact.
Yes, although Reddit was more mature by then and had some communities already.
I'd say we're not at a Digg point just yet. The ingredients are there, but I feel the next big crisis, whatever it might be, might be the push over the cliff that does it. Hopefully kbin and the Fediverse get to a good point of maturity by then and can welcome the more casual redditors without a hitch.
Thing is, though, Reddit was offering Digg users something new in terms of user experience. I'm not sure federated content is that "it" factor for many.