For someone just following a boglehead index whatever, it should just be business as usual. Treat it as any other crash. That is, do nothing except maybe rebalance stock/bond ratio to match once or twice a year.
"Being correlated" doesn't make it useless.
I think those skills will actually be rather useful now. A lot of them seem to be living off the revenue that talking about and selling their books on F.I.R.E. rather than the actual investments.
so some people that did nothing but sit on the beach after FIREing may be uneasy, but a lot of people transition into other fields that just aren't necessarily as lucrative.
They'll be fine; they've been enjoying sitting on the beach. More savings doesn't protect someone from a market collapse, it just exposes them further.
A rational long term investor - assuming the stock market was going to stay like this forever - would have avoided saving any money for the last few years and would probably have been sitting on the beach enjoying themselves.
Will this slow down a lot of early retirement plans? Almost certainly. However the market is not 0, lots of these people still have substantial amounts of money saved.