Hypothetical gambling question

You have $750,000 to your name and a group of you are in Vegas. This $750,000 is your life savings.

One of your party is hammering frantically on your hotel room door at 1a.m and when you open it he says "I need $500,000, I am out of money in the casino but am playing a game downstairs where I have a 7-in-8 chance of turning the $500,000 into $1m"

Would you lend him the cash?

He has no means of paying you back if he loses.