Stock prices should respond to expectations for long-term returns. Thus, short-term, even medium-term economic disruption is largely irrelevant unless seen to impact long-term returns. Short term events are relevant mostly to speculators.
Rational investors will know that while individual companies may fail, the market will always recover. Thus, an investment in a broad market index or fund is safe, even in the most crazy times -- i.e. you won't lose, as long as you are willing to wait for the recovery.