What broke Digg is exactly what will break Reddit. The 90:9:1 rule applies just as heavily to Reddit as it does to everything that came before it, including Digg. If you made a Venn diagram of Reddit power users to those affected by the shuttering of popular apps, the overlap would be immense, and I'd be willing to put money on it being the case too.

If you drive the power users away, nobody is sharing content or engaging in the comments regularly enough for the 9% of casual commenters to stay engaged and they leave - then the 90% goes because there's nothing at all for them to lurk around.