Yes, you need some insulin (via shots or natural) to live, every day, otherwise DKA + death occur within 3 days, guaranteed.
The question is, how much insulin? When you burn fat the metabolic pathway is different, but I think regardless of your diet, even if you're just burning fat from your own gut, your body is also synthesizing sugar and protein continuously which can get broken down into sugar so I believe exogenous insulin is necessary all the time.
Back on my other blog, we've talked about this many times, like, if you become super skinny, eat very very low carb, and low overall calories per day too, then even having a small-ish amount of c-peptides might allow me to get by without much, perhaps no, external insulin.
Exogenous insulin shots also suppress internal insulin production from what I've read (this makes sense, right? If you have an external reason why your sugars are lowering, then the body will naturally produce less because it just doesn't need to. Of course this assumes perfect control, which is impossible, even with a pump). Then the question is, is the super-tight control offered by a closed-loop, dual hormone pump system, actually ideal or detrimental towards beta cell regen? We don't know this yet. What we do know is that pump users don't spontaneously heal, despite having better overall control than non-pump users. So perhaps FMD is what's missing.
However, for beta cell maturation to occur (which is when the fun starts), they need to be challenged by glucose: this is known from the research on babies weaning (eating solid foods with more carbs and less fat content than their mothers' milk) and the hyperglycemia-induced beta cell replication study (shared on my blog). Elevated sugars stimulate beta cell maturation, replication. This is known.
There are lots of variables at play. Which takes me back to my question about how many carbs should be eaten in the re-feeding phase. It's likely a balancing act, I think.
More carbs/sugar => more IGF-1 => more regeneration post-FMD seems to be the flow.
But glucotoxicity due to hyperglycemia also stresses / damages / kills beta cells, so too many carbs is bad for beta cell survival. I'm still taking verapamil for that. But on its own, verapamil doesn't seem to be a cure, it (likely) helps boost c-peptides by a bit, but then other processes reduce this over time (auto-immunity kicking back into overdrive?).