Power law still applies. Most likely 90% of serious action is done by the same 0.1% contributors (same as it is on HN or reddit or anywhere else).

It may be a real difference if the 0.1% can be easily replaced, Stand Alone Complex style. Say they're all arrested one day, and a month after something happens (Julian Assange is extradited, there's a revolution in Iran, whatever piques Anonymous' interest). There's a good chance many people at the same time will think that something needs to be done, see that nothing is happening, and do it. Not as good as the "old guard" maybe, but they'll probably try.

We can't really know how well this replacement mechanism works...