If there is a crash, worry about the clearing system

"Never bet on the end of the world, because it only happens once, and even if it does, who are you going to settle the trade with?" - Art Cashin

The quality of the clearing system matters greatly, and we do not have to wait until the end of the world. There has been significant work in improving the clearing system of stocks and bonds and with the clearing of swaps. 

There are several added proposals that are being considered that should add to clearing safety. The goal for most of these rules is for more centralized clearing and more transparency, but there is also a need to have flexibility and allow for alternative approaches to risk management and clearing otherwise the system is sensitive to the single set of rules that control the system. A one size fits all approach means that the rules must be right. There is no alternative and no room for error. If that is the case, we should be more conservative with any rule changes.

Nevertheless, if you think the financial markets are headed for a crash, you should assume the system and institutions will crash, so trades have to be made to ensure you get your cash early. It also means that waiting until the bottom will never work.