It will not come to that point. There will never be a Bitcoin shortage. The value of Bitcoin could adjust up to whatever point it needs just to satisfy the demand and the necessary valuation when the entire world will be using Bitcoin. If the demand is rising so high due to the billions of people across the world using Bitcoin, the market will be assigning a bigger value to every Satoshi. There are eight decimal points in every BTC. It may happen that .00000005 BTC will be valued 1 USD.