I had gone through the FAQ, and through the forums. and I cant find anything for or against this notion that i got from somewhere... I might have dreamt it up...
Lets use Bronn as an example. When a character would be killed, stand bronn instead.
For some reason, i got the idea that the character is still considered to be successfully killed, only something else happens instead during resolution (Bron stood). Thus I thought Anguy would be able to respond (provided it is controlled by an opponent).
The question comes from someone asking about "Stay of Execution" and "Rhaegar Targaryen", Again I forget where i got this notion from. But it leads me to believe that Rhaegar could still trigger despite now being Morribund:Returned to hand.