Writer/Director Joss Whedon spoke to this scene in the director's commentary. In short, the goal was (from filmmaking perspective) to show that the fight was definitively over once Tony had made his hail-Mary sacrifice.

And then we get into the inevitable sort of "Queen bee, uh-huh we killed the head and all the soldiers fall down dead". I'm not proud of that either, Okay? It was necessary to make sure we understood that they didn't have to clean up for the next 17 hours by still fighting. So they could actually have their moment of triumph but it's a device that I'm not fond of (and probably shouldn't have brought up!).

Had they not had the "drop down dead" scene, they would have needed additional scenes to explain what happened to the Chitauri soldiers after the spacial fissure closed. There's also a great deal of difference between killing an invading army and killing a soldier who has no hope of escape.

Writer/Director Joss Whedon spoke to this scene in the director's commentary. In short, the goal was (from filmmaking perspective) to show that the fight was definitively over once Tony had made his hail-Mary sacrifice.

And then we get into the inevitable sort of "Queen bee, uh-huh we killed the head and all the soldiers fall down dead". I'm not proud of that either, Okay? It was necessary to make sure we understood that they didn't have to clean up for the next 17 hours by still fighting. So they could actually have their moment of triumph but it's a device that I'm not fond of (and probably shouldn't have brought up!). (MP3 Link)

Had they not had the "drop down dead" scene, they would have needed additional scenes to explain what happened to the Chitauri soldiers after the spacial fissure closed. There's also a great deal of difference between killing an invading army and killing a soldier who has no hope of escape.