Good point that the Fed has fewer arrows in their quiver. Then, though, the 2008 drop was because the assets being traded or valued were in many cases worthless - mortgages based on an ability to pay that in many cases was non - existent. Those holding the mortgages were going to default in mass, and the houses were overvalued too.
Now the markets are dropping because oil is low and the Chinese economy is slowing. In some respects, oil being low is not a bad thing. People drive more, buy larger cars, buy houses further from work, ship goods cheaper, perhaps travel more as costs are cheaper - all things that will drive the economy up. And cynically, it will just take another war, a few refineries closing, the oil reserves gradually depleting as companies drill less, before oil becomes more valuable. I don't see society moving significantly away from oil for another decade. One way or another I think oil will rebound - or the energy companies will diversify into something else they can sell.
I don't see the central banks caring more for the long term economy over short term profits, even if, as was proven with the mortgage crisis, they knew what they were selling was crap,
I also don't see the Federal government doing anything to rein in the deficit, which has been a significant weakness. During the last crisis, the Russians approached the Chinese to crash the U.S. economy. At the time the Chinese refused, because they perceived their economy depended upon selling to the U.S. But though our government knew this, it continues to spend. Most Americans seem oddly clueless or careless that you shouldn't spend what you don't have and don't insist on a balanced budget. In fact, anyone suggesting that is reviled as being heartless, or racist, or something equally vile. Meanwhile, others who've struggled to pay their way and save are reviled for not being willing to pay the way for others. I don't see the government or popular trend move toward making good choices - in fact the choices made after the last crisis often seemed to perpetuate the same practices and increase the risk. But that didn't stop people after 2008 from investing in the market and doing well. The central banks naturally will be more concerned with their survival than the U.S. economy, and the Fed will assist them because these entities have become so large that the Fed can't cover their collapse. It may be out of arrows for its quiver.
So yes, if things melt down, it could get very very bad. But in that worst case scenario, is there a place where $$ are going to be safe? Stocks will crash. If the banks go en masse, can the bond market survive? The dollar may be worthless paper. After all, we're hardly on the gold standard. Some have claimed the dollar only has held what worth it has because global oil is traded in it. Even if you have your dollars not in banks but buried in your back yard, what worth will paper have in such a scenario?
I'll admit to being very ignorant, and I have no solution of where to invest in such a fiasco. But if/when it happens, seems to me that it will be a much different game. And no one, yet, has a clue what that would be. Those who have made predictions as to such a total collapse, who have recommended doing things like investing in foreign currency (if the global banks crash, good luck), buying gold, or moving to some remote, self sufficient lifestyle are branded as kooks. Considering our economy collapsed in 2008 over banks buying and insuring mortgages as a good risk that were based on overvalued houses sold to people who couldn't afford them the definition of what is a kook in such a case is kind of amusing. Who is kookier, the average investor who looks at this house of cards and is skeptical, or the engineers of the house of cards? But right now, it is a game most companies who provide 401K funds, and most investors, are tied into playing.
Will the carousel stop and crash? Perhaps, maybe probably. Our country is very young in the scheme of things, and our financial markets based upon sometimes shaky principles. But for the average retiree or future retiree, WHEN this doomsday scenario will happen is more important, and WHERE to invest until then is the choice we all have to make. I wish our politicians, government, and banks treated the debt and the money they bandy about as if it were their own. Then perhaps we would be less vulnerable. A good reason to have smaller, more independent banks - but the Fed turned their backs on that scenario, preferring to consolidate into entities that are even more "too big to fail" than before. Again, I am far from being as knowledgeable as I could wish, but in such a doomsday scenario as you put forward, won't the game be very different and the question as to whether to buy or sell in the market minor in comparison?