Uncontrolled diabetes clearly shortens lifespan (and quality of life), but not as much as smoking does.
It is possible when Type2 is reversed and control by diet, that then having had Type2 does not have any effect on lifespan. But no one has enough data to say for sure.
(I see the usage of drugs for Type2 as being a way to speed up the improvement from a diet with radically fewer carbs, hence I support the use of drug along with diet. But aiming to get an A1C in the low 30s (5%) then reducing all drugs other the Metformin.)