In Of Mice and Men, is Curley's wife's death inevitable?

I would say that Curley's wife's death is inevitable in Of Mice and Men.

The way Steinbeck constructs the narratives of Lennie and Curley's wife establishes what takes place in the barn. Lennie had problems with his last job in Weed because he grabbed a girl's dress.  He has also shown a penchant to want to touch "soft" things that feel "nice" to pet.  Finally, Lennie had already seen Curley's wife and remarked that she was "purty."  

For her part, Curley's wife enjoys being the center of attention.  The ranch hands continually comment on how Curley's wife appears in the bunk house so that she can be noticed by the other men.  Candy says that she has "the eye" in the way she interacts with Slim and Carlson. When she is alone with Lennie in the barn, she recognizes that she has an "audience" that could listen to her story of wanting to be in "pitchers."  The combination of Lennie seeking something he sees to be soft and beautiful and her wish to be noticed by others makes their contact inevitable.

As has been the case throughout the narrative, anytime Lennie comes into contact with "soft" creatures, death is inevitable.  Mice and puppies perish under Lennie's touch. Even Curley's hand is destroyed when it comes into contact with Lennie.  The moment Curley's wife allows Lennie to stroke her hair, her doom is inevitable.  When she gets scared and tries to pull away, Lennie's grip tightens.  He breaks her neck as her screams intensify. 

There could have been circumstances that might have averted Curley's wife's death.  Had she not been in the barn alone with Lennie, she might have lived. If she was not so insistent on having an audience, there is a chance she could have avoided a dangerous situation.  However, Steinbeck shows that if we are not careful, our desires can lead to bad things.  Her desire to be noticed and Lennie's compulsion to touch define both of their personalities and set the stage for her death.