The inhabitants of the island do seem to genuinely believe the Swirly Hats are dead but these are One Piece's main characters. We all know better.
If their "death" is from an enemies fruit, what ever the affects are will be reversed one way or another. The way this chapter played up their demise though has me believing that for the most part they are just fine, no more hurt than the Guardians or Law's crew. I'm still banking on Brook causing some sort of illusion that caused the group to appear as convincingly dead as possible. Maybe Jack attacked Zou specifically because half the Straw Hats were there and left once they were killed. Forming a plan and staying hidden until the rest of the crew arrived could have been an easy way to pacify Jack's anger when it was clear only half the crew wasn't enough to deal with him.