What is the chance of cisco 3750x 24 port poe switch failure?
Anything is possible. What are the chance that the computer you are using now should fail? What are the chances that the mobile phone you are holding will fall and break? Sorry, your question lacks substance to justify a response in "details".
is backup necessary for this
I don't understand why you are asking this question.
My first question to YOU (or your school instructor) will be: How important is this switch in your network?
My follow-up question: How complicated do you want this "backup" to work?
