Season 3 Isn't that what family's for?

[verdantheart]

We don't know what would have happened if Katya hadn't called it off. It might be that Jack would have had a little talk with Sloane. We can't tell because we didn't hear that conversation. I have a hard time picturing Jack murdering anyone at Irina's or Katya's behest, though.

But Jack did not warn Sloane ahead of time because we have Sloane's message to Jack to vouch for that.