I would try 4-6 weeks on slin with the GH and then go 2-4 weeks off and get your blood sugar tested or just see how you feel during the 2 off weeks. Getting your blood tested is as easy as it gets and will tell you exactly what you want to know. You can even buy the blood tester yourself and the test strips for right around $100 bucks or so. But even without the blood tests, if you feel fine for the 2-4 weeks off then you may be adjusting fine and you can extend the next cycle or stay on for the whole time depending on how risky you want to get.
IMO, you won't become permanently diabetic even from staying on slin throughout the whole cycle of GH- but that's just my opinion. I can almost guarantee that you will have some major problems with abnormal blood sugar, both lows and highs, when you come off of that much time on slin and GH. What happens is that you throw off the natural homostasis that your beta cells achieve when your hormone levels are constant. When you throw slin and GH into the mix, then go off, you are basically confusing the hell out of your body. I believe that with time your body will naturally start to find that homeostasis again- how long I'm not sure and when you fool around with your endocrine system things can be very unpredictable.
If you decide to cycle or if you decide to stay on the whole time, make sure you taper your dose of slin down when you get to the end of the cycle so that you make it easier for your beta cells to start producing more insulin again- kind of like a smooth landing rather than dropping right off the radar and expecting your pacreas to respond immediately.
Hope this helps some- good luck!