Digg didn't "die" from a single change. It bled users over the course of multiple changes. The size of the waves was based on how many users were affected. The big wave was when they redesigned the whole interface.
I don't think Reddit is done changing, so we'll see where things go. I know that eventually they'll kill off the old interface, and that will lose a large portion of users as well.
Digg had bled users to reddit over the course of a few years before the big one. Many users had accounts on both for that period as well.
"This was on reddit yesterday" was a top comment on Digg often enough.