Yes, BTC oriented business could easily become defunct.
Mining is the perfect situation to take as an example, as it is purely Bitcoin related and depends upon currency conversion to cover operating costs. It becomes unprofitable around the $2-6 range if electricity costs are incurred and depending on efficiency. If the hardware costs haven't been recouped yet and the price drops below operating costs, the "business" either shuts down or runs at a deficit until all supporting funds are depleted. Either that or the currency price rises.
A Minskian collapse is a possibility. However, I think the difference between Bitcoin and contemporary currencies controlled by a central authority preclude complete failure. My thinking is that the decentralization coupled with self-regulatory aspects and the Satoshi unit being effectively indestructible (a la gold) mean that the decline is limited in a similar manner to stock liquidation.
Even if a company's stock goes to zero, the corporate assets still retain some value. Likewise, even if Bitcoin goes to zero on a foreign exchange basis, it will still retain some value within the Bitcoin economy. Granted, that would be extremely limited, but it simply refuses to die.
The intriguing prospect for this is that with such a reduction in perceived value, the participants will be thinned out heavily. That will make changes to the system much easier to propagate. Whether that involves adjusting the base inflation rate, raising the cumulative total or other modifications. It becomes a phoenix - reborn, as many times as needed... and the BTCs held continue to exist.
But this is not a bitcoin specific phenomenon.
True, but the underlying currency used is the issue here, not so much the particular business. Typical fiat currencies can experience complete loss of confidence and no longer have use. Bitcoin can experience the same, but it still doesn't cease to exist; it just temporarily goes to zero in relative valuation so long as the system integrity remains.
Think of a machine tooling company that goes out of business because the currency has gone into hyperinflation. It may have had to close its doors because of the situation, but a lathe or ceramic saw is still useful. Bitcoin's value could go to zero, but the system itself is still sound.
Or a car with a dead engine - the gas is still good...
Who knows, maybe Bitcoin is just a few years too early in trying to fill a void that hasn't fully presented itself yet.