Hi,
Sorry to hear about your father in law.
If his pancreas is shutting down it means that there is not enough insulin and his blood sugar is going high. They want to give him injected insulin to prevent it going so high.
You would not expect him to get low blood sugar unless he was given too much insulin. However, in his current condition, I expect they will just give enough insulin to keep his sugars at manageable levels.
With regards to treating his blood sugar or not (ie. inject insulin or not), this is a discussion you and he need to have with his doctors. At this point, keeping him comfortable and getting as much quality of life possible in the last few months would be a priority rather than aggressive treatment.
At this point, his body is already starting to shut down. I assume that if he because unconscious the medical team may not take heroic measures. Again this is discussion you and he need to have with his medical team.
Wishing you and him, and your family, strength and peace at this time.