They are a bit less important than they once were in terms of volume, but they are still massively interconnected with the rest of the system. There is zero chance they‘re just left to implode without governments and central banks stepping in.
They'll just disappear and the pieces of it be sold off. They're not that interconnected anymore since they've been selling everything the past few years.
I think the AUM comparison is something everyone needs to be careful of. Vanguard has a lot of AUM from me (from my point of view anyway), but it’s (hopefully) 100% passed through to security issuing organizations. They only get to rake a fraction of a percent from me for their operations.
Wayyyyy different than a bank with $billions in checking and savings accounts where they can do ??? with it.