After a devastating experience with one of my cats years ago, I swore I would never be without pet insurance again. My beloved rescued FIV cat was diagnosed with liver disease, and his only chance was intensive care, which we simply could not afford. The vet did what they could, but having tried some natural remedies, our only recourse was to have him put to sleep. I did not feel he had been given an adequate chance of fighting, and he was a tough cat.
I made sure that subsequent rescues had insurance, and I have no regrets. When another of our cats developed IBD/intestinal cancer we were able to ensure that he was comfortable and that we had offered him every possible treatment available, short of chemotherapy. Knowing that he was living the last 6 months of his life to the fullest was very important to us, and those months turned out to be the some of the most precious. I was able to care for him without stressing over the cost - which was only a fraction of the total bill.
I advise all my friends with pets to have pet insurance, and I treat it with the same urgency as I do our own health insurance. We are all subject to sickness and the unexpected, and we cannot all afford such high bills, so if pet insurance is available to us, we should utilize it.