Well I should say that I have not heard of any actual instances of harness cracking causing a fire. But I feel wary when the metal wires are exposed, it is possible to have a short or a spark.
But I would definitely NOT discuss with your insurance company ... if your car does ignite, you don't want them to know that you had prior knowledge of an electrical fault and did not repair it.
Disclaimer: I am not an electrician, a fire safety professional, or an insurance adjuster so my advice may be worth what you've paid for it.
