I'm so sorry to read about your loss.

There are similar stories to yours other places on the Internet. Many carriers have stop transporting pets in the cargo holds during summer as a result. I've heard carriers have been fined under the Animal Welfare Act. The USDA is supposed to enforce the act. You might want to get in touch with your local office. You may want to share your story with the media too, if anything, to make others aware of the risks.