> if Robinhood couldn't meet the new deposit requirements, I think the existing trades just wouldn't settle (and obviously they wouldn't be accepting new ones)?

Defaulting on clearing obligations is the old school way for a brokerage to go under. The moment that happens, customers’ funds and assets are segregated and what is left goes into receivership. The parent company would then file for bankruptcy protection to avoid being stripped for the broker-dealer.

The point of a clearinghouse is that trades always settle. Certainty in that is paramount. Individual members’ survival is secondary. Which makes sense since it aligns interests.