It's actually a quite complex question that does not have a clear cut answer. In case of T2D you can 'go into remission' meaning you can get your blood glucose levels to 'normal levels' with little or even no medication (T2Ds are not necessarily using insulin, they can also use medication that increases insulin sensitivity such as metformin). Generally weight loss, exercise and a healthy diet are what allows them to accomplish that and a keto / low carb diet can definitely help there.

For T1Ds I'm afraid even a keto diet still contains too much carbs to live healthily without insulin. Unfortunately if your body has fully stopped producing insulin and you don't take any artificial insulin your life expectancy is not looking good regardless of how you live.