Unlike Wildfire Assault, Valar Morghulis does not have the stipulation that killed characters cannot be saved. Does this mean that and card (including an attached duplicate) that could save a character can be used to keep them out of your dead pile? I'm playing the dragons/Daenerys strategy with duplicates on all of my core characters, so would they be safe from Valar's effects if I discard the duplicates?

Yes, you can use save effects against Valar - including dupes. You can use (appropriate) save effects against any effect that removes a character from play (unless, of course, it specifies "cannot be saved").

Cool, thanks, that's what I thought.