House Greyjoy only.
Response: After a character card is discarded from an opponent's deck, put that card into play under your control. At the end of the phase, return that character to its owner's discard pile.
If the characters which are put into play by River Raid are killed, they are placed in their owners dead pile and do not move into the owner's discard pile at the end of the phase, correct? My reasoning is that since the last sentence refers to a character and not a character card that it would not work on a card in the dead pile.