Trying to put people into 2 little boxes insulin dependent/ non insulin dependent isn't helpful. That's why they abandoned using those terms as labels in 1999.
It is recommended that the terms "insulin-dependent diabetes mellitus" and "non-insulin-dependent diabetes mellitus" and their acronyms "IDDM" and "NIDDM" no longer be used. These terms have been confusing and frequently resulted in patients being classified based on treatment rather than on pathogenesis.
WHO 1999
. A person with T2 probably always produces some insulin but as SId said, it often progresses with more beta cells being killed off, and or more insulin resistance. People who have relatively too little insulin will depend on insulin injections just as much as those who have none at all (actually 2/3 of T1s also produce a tiny amount of their own) Most people using insulin are not T1 but T2 because there are many more people with T2 than T1.
If glucose levels are not lowered, a person with T2 doesn't normally develop DKA (though some do). However, untreated,they may develop HHS,( Hyperosmolar Hyperglycaemic State) basically DKA without the ketones . It only takes a little insulin to surpress ketones. If untreated this will result in coma (HONK). The death rate from HONK is very high.
Pre insulin there were those with what we now call T2 who survived on very limited diets. There were others that this didn't work for. Of those who were severe enough (and probably rich enough) to be seen by a hospital , their survival rate at aged 50 was about 8 years, compared with about 2years for children. Just as with the younger patients, the cause of death for most was cited as 'diabetic coma'. ( some would have been late onset T1s so probably DKA, many probably died of HONK). It wasn't until after the introduction of insulin that life was prolonged and the cause of death for most people with diabetes at this same hospital became CVD or other diabetic complications. (source Joslin 1951)
From 1922 to the late 1950s, if diet and exercise failed... and for many it did, insulin was the onlsy available treatment. It wasn't until then that other drugs became available, and as previously mentioned, in many people diabetes progresses and eventually, no oral drug will work .
And of course there are far more varieties of DM that T1 and T2, though often doctors only use the 2 boxes. Some of these other types also depend on insulin for survival.