Legally, you are only liable if the cat had the seizure and passed away due to something you did--e.g. you used some product on it which caused the seizure; somehow shook it or held it in a such a way as to trigger a seizure (assuming that is possible); etc. If you did not cause the seizure, you would not be legally liable, though it is sometimes worthwhile to pay, even when not liable, to avoid bad publicity, loss of a business relationship, etc.