First of all, hell would freeze over; we'd have bigger problems! :)
I think speculation about unlikely events isn't very productive; for instance, whatever made them 'suddenly' do whatever (we've discussed before why it appears that the savings rate in the US is "lower" than in other places) probably either would cause other things or would have been caused by them -- that might have far more interesting consquences.
Example: what if the tax advantage of IRAs was removed?
/jordan