Yes.
.y=zorder
Z-order won't help get the kind of 2.5D look Don't Starve has. It also won't help with the perspective shifts or camera rotation.
Is Don't Starve basically a 2D or a 3D layout which just has a camera which is under a certain angle? I believe it's 3D, still unsure though.
Do you think Construct 2 is capable of such a game? The collisions could be for example just the bottom of trees, bushes... So that movement is possible behind the trees on different layers, that would give the world sort of an effect of the world being 2.5D-ish. =]]
It's possible to do that kind of gameplay and do those kind of collisions, sure. You'd have to use one of the 3rd-party 3D plugins to get the look/camera movement.