He definitely needs to apologize, or the situation needs to be explained in greater detail. I'm not one to say that he should be leaving because of it. He obviously felt confident enough to take it, and right now we need some confidence in this team. Unfortunately, he chose the wrong time to step up in this game.
Of course if he would have made it this would be a different story. But he didn't, and now his confidence is probably going to suffer as well, which is good for no one.
A similar situation occurred when Dempsey chose to take a penalty and missed for the USA when Donovan was always the designated penalty taker. The difference is, it was obvious that Klinnsman had chosen Dempsey for penalties and we were already up 2-0. Dempsey got some flak, but it didn't cost us the game, and people were more pissed at the miss than his character obviously. Maybe it's a lot different actually.
Either way, I hope we keep Mirallas, but I hope he learns a great deal from this. He should listen to the team next time.