the more important question would be "how can Bitcoin prosper when they can get lost forever?"
if the available amount is decreasing by time.. what would be a critical mass that is needed for a currency worldwide?
Since you can move the decimal as you need, any amount of BTC is enough for the world. You would then use like 0.000000000000000000001 btc, we will make a client that wil say that it is 1mini-BTC and you are fine
After all, "how can gold prosper when it can get lost forever?" What about all the gold in the ships that sunk? For thousands of years it was lost!