Chalmers argues that discovering that the simulation hypothesis was true would not show our beliefs about the existence of physical objects to be false, but merely indicate a surprising truth about the nature of reality. So he would say that yes, the rock does exist even if the simulation hypothesis is true.
I think this is relevant to some of the discussion here: David Chalmers, The Matrix as Metaphysics.
Chalmers argues that discovering that the simulation hypothesis was true would not show our beliefs about the existence of physical objects to be false, but merely indicate a surprising truth about the nature of reality. So he would say that yes, the rock does exist even if the simulation hypothesis is true.