Even Type I diabetes - once insulin injections are started the islet cells normally partly recover and start producing insulin again. The 'best practice' approach is to suppress these as fast as possible using a high carb/high insulin intake because their unpredictable contributions make blood sugar management difficult. But there are indications, at least for a percentage of Type 1s, that it might be possible to provide supportive low level insulin on a low (not no) carb diet for a time and then back off the injected insulin completely once the cells recover. The damage to the islet cells would require faithful adherence to a low carb diet and blood monitoring would still be necessary.

That is, analogous to some kidney diseases, it is possible to have a crisis in which the cells shutdown but with supportive dialysis/insulin which takes the load off the cells for a while the stabilised condition could then be managed by diet for an indefinite long period. Other people, the disease is quickly progressive and standard treatment would be needed. Although, I still think even these type I diabetics should be educated to eat low carb and use minimal insulin rather than eat what you like 'because you deserve it as a victim of this horrible disease' and then cover with insulin as required. This leads to Type II like insulin resistance on top of the Type I deficiency.

Of course, with the obvious downsides, no one mainstream has much interest in experimenting with a supportive crisis care/diet+testing approach.