Purely as maths, I'd be inclined to look at it as putting a hold on the countdown for a ticking time bomb. Every day you're good, and keep yourself mostly in pre-diabetic to non-diabetic ranges, that clock stays stopped, and you bought yourself another day of your life before complications set in. On the days when you're naughty, you're letting that timer count down. If you're naughty one day a month, it'll take 30 years to hit the complications that might otherwise have caught up with you in a year. if you're naughty one day a week, it'll take 7.
I'm sure, in reality, it doesn't work like that. Things are rarely so black and white in real life. Most likely, the clock is always running, and you're merely slowing it down on days when you're good and speeding it up on ones when you're not. Also, if you can keep your levels low, certain things, such as neuropathy, might improve. It may be possible to run the clock backwards, in respect of some complications.
I'm budgeting for being on this planet for another 25 years or so. My goal with respect to diabetes is to get there without any serious complications. But deterioration on various fronts is pretty much inevitable. I think that's a reality that sets in once you pass 40.
Of course if you hit very high figures, you can be in immediate danger. Certainly, 30+ and you're looking at an immediate risk. Possibly quite a bit lower than that. Unregulated, I believe my body starts peeing it out in the high teens. My HbA1c result suggests my average blood sugar was 12mmol/L prior to diagnosis, and that was with an addiction to Kit-Kats, Aldi fake Mars and Snickers bars, and big tubs of Celebrations.