The Debate To End All Debates – does fate control our lives or do we have free will? – takes center stage in this novel. And in The Return of the Native we get frequent hints that free will is losing. People seem to play parts in a very old story here, and events and nature constantly conspire against people. Yet characters do make choices. Unfortunately for them, these choices usually make things even worse and seem to have little to no effect against the larger forces at work in the novel, such as the unaffected heath (which pays no mind to the people on it) or fate (which seems to constantly screw everyone over).
Free will is not so much absent as it is defunct and ineffective in this novel. No one makes very good decisions and the decisions they do make are perhaps dictated by a higher power of some sort. And what is this power? Maybe it's the weight of the past, perhaps it's human nature itself, or it could be the heath or even God. The novel never makes it entirely clear what fate is, but there's is a strong sense that our characters are living out events that are largely beyond their control and that their own choices either have little impact or only help to further doom them.
Fate is the major driving force of the novel, and the characters here largely lack free will.
The characters give too much credit to fate; their own poor decisions cause problems.