For the topic yes there are only 21 million bitcoin that can be mine and some bitcoin could be lost through the years. If bitcoin becomes really expensive like 1 bitcoin = millions then remember that it has satoshi.we do not know but there could be a time that 1 satoshi can equal to one dollar.Maybe at that huge population that bitcoin will handle it will be satoshi who will be the main trade. If bitcoins stayed obviously! It will reach 1 million in no time.But I think we should first consider if it stays or not before considering the possibility of it reaching millions.