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...
If we go with the fact that Anonymous is infact a true distributed environment, then the replacement mechanism will be very easy. I think Anonymous is a kind of humanized group-comm architecture sans a coordinator.
You're overestimating the uniqueness of Anon. Most communities nowadays don't have coordinators. And Anon doesn't have limitless communication channels, only about a dozen. For a site/software to be a good choice, it has to be already in the "hivemind". Ask 10 Anon tot tell them 10 places where they hang, and the most common choices are the (only) ones that are viable.
There is a unique feature though - the anonymity. This could really make a difference if things get serious.
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...