Leave it exactly as it is. Complete with the slightly less than believable reaction by Deadeye. Very campy, almost fake.... It's PERFECT as it is. Now, now, don't wet your britches, I'm not finished yet. Hear me out....
Further along, in the Elder game, it is revealed that Sadie's death had been a primary objective for the Dominion for some time, a highly wanted women. Perhaps she offed some Dominion hotshot while working as an enforcer? As it turns out, her death was faked as a means of getting the Dominion off her ass while she was pregnant, vulnerable/with a newborn child. Deadeye's rather off reaction being due to cowboys generally being bad actors. Now no longer pursued, she's free to recover and get ready to assume her new job as an Exile assassin, lying in the shadows, hiding undercover, dead for all anyone knows, hitting the Dominion when they least expect it.
So how does the big reveal come about? Simple. Make it not an Exile, but a Dominion storyline quest. What? Yeah, that's right. This interweaves the stories of both factions in an incredibly deep and introspective manner, while encouraging players to play both factions to get "the full story". It also references events that the player had probably forgotten about til now, creating a great level of surprise and depth. So what's the quest about? In the time span it took you to reach level 50 and hit that point in the quest, she's recovered from her pregnancy, her daughter safe. Obviously, she's not exactly happy about the Dominion trying to kill her child and now? Now, she's pissed and out to return the favor, by personally putting a bullet through the skull of Dominion noble, Malvolio Portius.
Your job, as the player, is to prevent the assassination, the quest's final phase being an epic boss battle against Sadie and her mad skills, which of course, concludes with the ship/outpost/asteroid the quest takes place on blowing up spectacularly, you and Malvolio barely escaping, with Sadie disappearing, leaving whether she survives the event a mystery...for now. Perhaps Mal gets injured, a somewhat disfiguring scar added to his face maybe, as a way of updating the characters as the story goes on of course. This of course, leads to a quest later on in the game's development where Malvolio, hell bent on revenge, goes after her husband, Deadeye, deploying a crack team of ICI agents to get revenge! Maybe Sadie comes out of no where and, with a team of Exile players, tries to rescue her husband? So many great possibilities with awesome rivalry potential!
The result is a huge series of quests detailing the feud of revenge and spite between the Brightland family and Portius, along with the rest of the Dominion nobility. Everything is explained, everyone is satisfied, cutscenes and voice acting that already exist don't have to be completely redone. It also provides a big, sudden, crazy reveal for the players and of course, gives us an excuse to fight alongside/against all these absolutely amazing non player personalities that Carbine has delivered to us. In between quest releases, it'll even foster all sorts of cool Lore debates in the meantime. Did Sadie survive? What's Portius' big evil plan? Etc.
Just a thought here, as it basically solves....you know.... everything.