Bose,
1) 7.9 doesn't mean a lot without knowing if it was a fasting test (not eaten for 12+ hours), or a test 2 hours after a meal. As a fasting test, it is just about classed as T2 diabetes. If it's a measure 2 hours after a meal, it would be classed as pre-diabetes. It's not a very high level and can probably be treated with diet and possibly metformin, but you need to consult a diabetes healthcare professional. My knowledge is limited through having a family member who was diabetic for some years, but this isn't a diabetes forum, and if the info I gave you isn't correct, there may well be no one here to say so - you should seek help on diabetes from a relevant healthcare professional. If your dad is diabetic, there are other things that should be done too, such as retinal eye checks, checks for injuries to hands/legs/feet which can go bad before they get noticed, good professional nail grooming (feet in particular), always wearing footware to protect feet, etc.
While my relative had diabetes, I used to test myself periodically because it's well known for running in families. I now test myself monthly again since I started on HT, with that being known to be a significant risk factor.
2) None of us will know anywhere near enough about your father's case to answer this. Even your oncologist with access to all your father's medical data could only give you a very wide guess, even if they're willing to do so at all. Some people manage with metastatic cancer well over 10 years on hormone therapy. Nerve damage due to things like pressure can continue improving for months after removing the pressure - it doesn't usually fix itself instantly.