He wouldn't left himself open to that left hook.. in the first place.. so the question seems to be useless..
I don't think anyone at 168 can take a flush shot like that without getting KO'ed. The trick is to not get hit by it...
First of all Bute would never have gotten hit by that left hook because of his defense, but he had gotten hit he would not have taken it solidly. Bute would have stopped Kessler...............and Bute would have been landing on Kessler so often that Kessler would have been too busy surviving.............
Doubtful he would be able to take it, but even more doubtful that Kessler would land it on Bute. It wasn't exactly a super-compact shot.
I doubt Bute would get hit by that in the first place. And also I doubt Kessler once hurt against Bute like he was against Green would survive.