“What happens if CBT doesn't work for insomnia?”

First of all, you may want to talk to you primary care doctor about your insomnia to determine whether you have undiagnosed underlying medical condition that may contribute to anxiety manifested in having insomnia, also discuss your nutrition as they also may contribute to anxiety that exacerbates insomnia. If your PCP rules out medical reason and thinks that psychological factors that cause your insomnia, you also want to find therapist who specializes in insomnia treatment as not all therapists are trained in CBT for insomnia and there are different levels of expertise and training. Best of luck!

See this link...
https://consumer.healthday.com/sleep-disorder-information-33/insomnia-news-625/desperate-for-shut-eye-710546.html