Yes, he lost all of his money in risky financial undertakings (stock market, in your example).
Nice example of this slang phrase was in one episode of CSI Las Vegas (7x21). Forensics found a dead body of very famous boxer in the swimming pool of some night club in Nevada. Owner of this club was nervous, because of the cops presence. He was afraid that he will lose his customers..He said:
I know a man die here, but dead is dead. I'll lose my shirt.
regards