endtherapture: At the end of the epilogue did you let Letho live, or did you kill him?
Both. Twice. And I'm still not sure which one is the best choice. One the one hand, there's no question that objectively he needs to die, for a number of reasons:
- He thinks nothing of murdering innocents if it helps him reach his goal, such as killing the monk physician to ensure that his cover isn't blown, or an entire squad of elves when Cedric refuses to join him.
- As Sile points out, he manipulates everybody that he can. Expertly. When he encounters someone that he can't manipulate (such as Iorveth), he tries to kill them instead. Perhaps his behavior at the end is just an elaborate attempt to manipulate Geralt into sparing him.
- He thinks nothing about accepting the mission to sow chaos in the North, nor of framing others (sorceresses, Geralt) for his deeds, assassinating people for money, or backstabbing his supposed comrades (Sile with the flawed diamond). He thinks so little of that last one, in fact, that he describes it as a "prank".
- He only "spares" you in the first fight if Geralt starts winning it. If you don't fight well enough he won't hesitate to kill you (perhaps this is an oversight on the part of the programmers, but after getting killed by him at least a dozen times before I finally "won" the fight I didn't feel much gratitude for his sudden generosity). Plus, he instigates the first fight even if you say that there is no need for violence.
- Though he says his intention is to disappear, there's nothing to hold him to his word, and no reason to think that he is being honest. Letho clearly does not have any hangups about lying when it suits him.
- Geralt mentions that "witchers on the Path should help each other", but Letho renounces the path in the first encounter, so he's not entitled to any special consideration for being a witcher.
On the other hand, killing him just feels wrong (or if not wrong then certainly empty). He and Geralt were friends once and share a history together, and there's something about the way that he reaches out to Geralt as he dies that just makes the victory feel entirely hollow. It's just kind of like "okay, he's dead now, but what did that really solve?".
I don't think Geralt gains anything personally from killing him, so that just leaves a mountain of evidence that says that yes, he should die, and the question of whether or not it's appropriate for Geralt to hand him that sentence. From what I can infer about Geralt's personality, I'm not convinced that it would be.
Although, Geralt's role in the world is, as he often likes to say, "to slay monsters", and a recurring theme through both games is that you judge a monster by what's on the inside. And Letho's cold indifference and his actions throughout the story make him probably the second most monstrous major character in it, by my measure. First place goes to the Lodge for their arrogant scheming, their corruption of Saskia, the inept way that they allowed themselves to be played by Letho, and their granting of permission to Ms. Glevissig to nuke an entire battlefield full of troops because she felt that her influence over Henselt was threatened.
So in that sense, perhaps Geralt has a professional obligation to slay Letho, even if the victory is hollow on a personal level?