Here’s an article about monogenic diabetes - which is apparently 1-5% of young people who are diagnosed as T1. It’s an inherited condition that isn’t autoimmune in nature. Also, the article discusses beta cell function in longtime T1Ds.
“For decades, scientists believed that all beta cells eventually are destroyed in type 1 diabetes. However, earlier studies of Medalists and other sets of longtime survivors had proven that small numbers of the cells still appear in all individuals with type 1 diabetes.”