OP, if your friend would have won that night, doubled his money from all-in salary bet, would you then create "Do gamble with your full money" topic instead? Imo gambling is not about do or dont go all-in, but to be responsible gambler and dont fall under emotions. If this was your friend, then where were you when he was loosing all the money? Why dont you helped him as a friend?
There is also other side of the coin - your friend is now more experienced than you. He has already burned with gambling and you know only theory. He will find a way to solve his financial problem till next salary, but you wont be having such life experience.