Bitcoin's value is reflected solely through the price mechanism, because of the fact that it trades on the open market without any central entity to regulate its price movements.
When there is excess demand that can't be handled based on the supply, then the price will adjusted accordingly upwards. There won't ever be a stage where bitcoin is unusable because of low supply or high demand, because we can infinitely divide bitcoin into subunits of account. So no, a shortage is not possible, even if substantial amounts of coins got hacked, because bitcoin isn't a good - it can be divided and still used in the same way.
However, long term I do see adoption playing a big role in pushing aggregate demand for bitcoin, because after all you do need BTC to carry out transactions on the bitcoin blockchain. And that's a reason why I'm quite optimistic about the long term investment aspect of it as well.