Whitney is the youngest ranch hand who is there when George and Lenny come to the farm and then is gone without any farewell or "todo." This "easy come-easy go" role makes him more like an extra than a real character. It appropriately reflects the precarity and the vagrancy of the migrant workers, who drifted from farm to farm, picking up odd jobs wherever and whenever needed.
This is why George and Lenny's friendship is so dear. Their loyalty to each other breaks this isolation. As Lenny makes George "tell it," they are no longer doomed to be alone: "Guys like us, we not like them, 'cause we got each other..."
So what happens to George after Lenny's death? He might be able to go in with Candy after all and buy the farm, but what would be the point? Steinbeck leaves the denouement open to the reader's speculation. However, one thing is sure - without Lenny's companionship, in his heart George joins the ranks of the true migrant "loners."