Humans are the resilience in any system. No system is ever perfect, and no system will ever be. I think we'll be fine.
They do this all the time. There are quite a few pre and post-trade checks enforced by the exchanges. The net result is that if things go wildly wrong, trading will most likely stop.
This is part of the reason why Knight Capital's implosion had such a minimal effect on anything besides Knight's shareholders.