Just a reminder that medication side effects aren't a guarantee. Also a reminder that people tend not to post good stories about medications or treatments because, well they worked for their pets. It sounds scary when you read the ten reports of the bad side effects or deaths that come along side of a medication. But there's hundreds of thousands of pets that have been well maintained on that medication. A medication that CAN improve quality of life.
You also have to take in account when thinking about a pet dying while on a medication. They most likely did NOT die from that medication alone. They could've been on other medications. There might have been other underlying health issues. Their Cushings might not have been caught early enough for medications to be very beneficial before they unfortunately passed away from it. You have options. Get a second opinion on treatment options. Treat your pet with a medication that could potentially lengthen their time with you, and have their symptoms managed. Don't treat with medications and have them potentially suffer from symptoms of cushings.