Since the first part of this is an opinion-based question, I can't necessarily answer it for you. Instead, what I'm going to do is list the events that follow, which Curley's wife's death make "inevitable", and then ask you a series of questions to help you build an opinion.
A quick note on the word inevitable: it is defined as "certain to happen or unavoidable".
Let's go through a brief summary of the inevitable events following the death of Curley's Wife:
- Curley's wife is lonely and is accidentally killed by Lennie when he strokes her hair too hard, at which point she pushes him away, he panics, and then he breaks her neck.
- Lennie runs away to hide at the river, the site of the first scene, where George had told Lennie to go if there was any trouble.
- Candy discovers Curley's wife's body and first alerts George, then Curley. Curley leads the men on a hunt to find and kill Lennie, but George deliberately misleads them and then goes to find Lennie himself.
- George finds Lennie at the riverbank and soothingly describes the farm where the two of them and Candy will go to live, and then George shoots Lennie in the back of the head.
- The men arrive at the sound of the gunshot, and George lies to them, saying he killed Lennie in a struggle over the gun. Slim, whose belief of George's story is ambiguous, comforts him and tells him that he did what needed to be done.
Now I'm going to ask you some questions to help you form an opinion on the conclusion of this novel:
- Do you think that Lennie returning to the riverbank was the right thing to do? Why or why not?
- Do you think Candy telling George before telling Curley was the right thing to do? Why or why not?
- What might have happened to Lennie if he had been first discovered by Curley and the men? Why do you believe this?
- Do you think it was possible for George and Lennie to escape and start over? Why or why not?
- Why does the novel open with the scene at the riverbank and then close with it? Consider the events that drive the men to the riverbank on both occasions.
- What else could George have done in this situation? Do you think that, as Slim says, George did what he needed to do?
- Just because something has to be done, does that make it inherently right?
In terms of the second part of this question, much of the novel Of Mice and Men revolves around the theme of the American Dream. Steinbeck's perspective on the American Dream was not a positive one; in fact, many of his works depict characters struggling desperately and honestly to attain the American Dream, but in the end being defeated. The conclusion of this novel is most likely a commentary on the American Dream from Steinbeck's perspective.