[Corvo doesn't know that the Outsider has to be killed. He's not going to help Daud do it, but he's not going to interfere beyond a few words, either.

At the last part, Corvo looks up and smiles a bit.]

I don't care how old or weak you look. You're not fooling me with that. I'd have a knife on me if I was standing at your deathbed.

[Because no matter how old Daud gets, Corvo is never going to underestimate him.]