"So a major stock market 'correction' which devalorises vast sums (was it $7 trillion for the dot.com 'crisis') would represent such a state. [i.e. a crisis]"
Well, if that was a crisis, it did not seem so bad.
On Patrick's/Cox's definition of crisis as the moment when a major intervention from outside the system is needed, I would have thought on the Marx-Lenin-Mattick definition, the system has been addicted to outside interventions to sustain accumulation for more than a century. The welfare-warfare state is just such an intervention.
Will the current subprime collapse lead to a generalised market failure? We will see, but it does not seem likely.