It's worth while reading the literature on pre-insulin treatments, but for type 1 diabetics, the answer is: you might be able to live, if just, for a while (a decade or so), but lifespans are greatly shortened. Probably depends exactly on the particular characteristics of the disease for a patient.

I thought this was a neat discussion: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3062586/

A transcript of a speech Joslin gave https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1827782/pdf/can...