I would suspect, assuming he had nothing to eat, that his blood sugar would be quite low. Ironically, and possibly the salvation of diabetics caught in a survival situation, near starvation, a brutally restricted diet, was the original method dealing with diabetes before insulin was isolated. Even without testing of blood sugar it is sometimes possible to roughly manage blood sugar minute by minute by diet alone. Using many tiny low-calorie meals and watching the response. I doubt anyone could do it alone, the trip would be a constant ride between near coma and drunken abandon brought on my low sugar, royals had 24/7 caretakers, but it shouldn't be impossible to sustain life.

The general trend managing diabetes long term through diet is gradual weight loss, slow weakening and death. Type one, early onset, diabetics tended to die young even when they got intensive nurturing and healthcare that was only available to royalty.

Type one diabetes, along with hemophilia, was one of the royal diseases. Poor diabetics died out too quickly before insulin was isolated for the trait to be transmitted.

The good news is that at room temperature insulin is usually good for 28 days and the major disaster relief organizations have made insulin and diabetes a major subset of their efforts. The 28 days gets you through the initial emergency, secondary crisis and into long-term management and recovery.

Your right that insulin dependent diabetes is a major issue that will color every movement and action. But the insulin itself, and those 28 days, allows planning and sound preparation to carry the day and means the situation isn't hopeless. Even in the middle of a major disaster.