There was no financial loss. The surrounding press attention may have even helped sales. I still remember the news at the time a decade later. The real cost is the ordeal he put the people at Valve through.
Probably. Background: Half-Life 2 was contending with Duke Nukem Forever for the greatest vaporware title ever, when Valve released gameplay footage and a definite release date. The half-done state of leaked game and the subsequent one year delay caused people to think it might never ship.
Of course, when the game finally came out to rave reviews, all was forgiven.