if healthy people can drop coverage altogether and still buy in right before they need it (which is the rational thing to do),
and if high-risk people can do the same, and without paying higher premiums despite the probability of higher medical expenses,
the insurance companies are screwed. they won't have a premium base that will offset their risks properly. So unless they get federal subsidies they are done for.
see, I think this is part of the liberals plan to create a single-payer system. they got the insurance companies to buy Obamacare based on the mandates, but if the mandates aren't enforced (or are legally unenforceable) the insurance companies will go out of business.