I just got this question in my mind. What will happen if no one knows about the pasword of his/her acount will it posibly deduct to the main supply of bitcoin? Example bitcoin was 21million supply and one man got 1 million bitcoin he was holding and suddenly he died no one can open his wallet is it posible that the remaining 20 million bitcoin forever and yes, the 1 million bitcoin of the dead person will still exist, but won't move anymore because no one can make them move from a wallet to another.
This, so far, explains too why bitcoin supply is limited, and decreases with time. Now it's compensated by btc mined, but mining won't last forever (bitcoin income for miners decreases every 4 years).