User blog comment:TheDoctor230/Laurel Again/@comment-25224899-20160607154340/@comment-3221148-20160607171418

Not really, because Darhk's attempt showed that he wasn't bluffing when he threatened Quentin. However, if Laurel Lance survived the attempt, Darhk could have strongmanned Quentin into working for him and spying on Oliver, again. Which is why, I think, Laurel asked Oliver to help him fake her death and promise to keep it a secret.

I don't know what other promise would be so important that they'd cut the scene, tell that we'll see it in the future, yet not show it in the season finale.