You are forgetting one very important thing. It is usually some time before most individuals are actually diagnosed with diabetes, especially Type 2. In this intervening time when your blood sugar is out of control and you don't realize it, you are doing unseen damage to various parts of your body.
How this damage progresses or affects you in later life is the $64,000 question. So it is easy for me to tell you that with if you control your sugars, you theoretically should be relatively healthy, but who knows what damage you may have incurred before you came under control!
In any event, why buck the odds. We all know that if you let your blood sugars go out of control nasty things will eventually happen, so just don't do it!! Will this avoid any and all complications....who knows! But its better than the alternative.