In ''Call of blood : The Short segundo Life of Bree Tanner'' there's something I didn't understand, can anyone help me?

I was wondering, how is it that when Riley comes back from his meeting with Victoria (where Diego was supposed to tell him about the sun thing) he tells Bree that Diego is with Victoria and all and he gives her the message from Diego: ''Tell Bree I found out what our secret oath would be, I'll tell her in 4 days when we'll reunite'' (or something like that) BUT Diego is supposed to be dead (that's what Bree figures out during the battle since she doesn't see his body o anything).

So I don't get the fact that Diego is dead if he gave this message to Riley (a message only Diego could have dado since, except from Bree, he's the only one that knows about the secret oath)...