It was definitely a blind lucky punch from Garcia that cost Khan this match. But on the other hand he knew that's how Garcia fights, during the exchanges when the fight is close and personal he throws left hooks like this and hopes to land one. Khan could have won with the decision due to his speed and he did own Garcia for 2 1/2 rounds. But seems like he wanted to go for a knock out, something that he promised during a press conference. Could it be argued that he got caught up in the racist remarks made towards him and acted emotional and fought up close and personal with Garcia like they wanted him to?
I don't think his career is over, he is a clean boxer, no performance enhancement drugs. Unlike many other boxers. People like him cuz of that. So he suffered two or three losses, not a big deal, he can win some easy ones meanwhile while training harder, and then it's just one good fight that he needs to win and people will have forgotten of these two defeats.