Regina execution, version 1
Rumpelstiltskin watches as the arrows fly towards Regina and for all he knows, intellectually at least, that he needs her, needs her to cast the curse, all he can see is Belle. His beautiful Belle, huddled in one of Regina's cells, bruised and battered, so thin… She's back at the Dark Castle now, but she hasn't said a word so far, just clung to him and whimpered when he left her.
A mere flick of a finger counters the Blue Fairy's spell, after Snow White cries out, and the arrows find their home buried in once proud Queen, as she takes her final, stuttering breaths, Regina spots him, and the look in eyes, even as they fade out, says she knows that he killed and more importantly, knows why.
Regina's execution, version 2
Snow feels her breath come quicker, as she makes herself watch Regina, who is watching the archers. Part of her, the sweet, kindly woman part, wants to stop this. Killing is wrong. However, there is another part of her, a part that is now the Queen of this kingdom, and as such, responsible for all the lives within. As princess of this land she had to stand by while Regina slaughtered villages searching for her.
So, with a heavy heart, and her chin locked to keep it from shaking, she says nothing as the arrows fly, says nothing as they strike.
This is justice.