Delaying graduation requires a new defense, which means that your first defense failed. There may be many reasons for the failure of the first defense, and your paper may need to be revised. That hasn't met the requirements of graduation, such as poor performance in defense and unanswered questions.

Therefore, you need to make a second defense, so that you can continue to revise your paper and improve its quality, and you don't have to rewrite it with another topic.