It really depends on the individual. Look at Dr Bernstein (not that Im recommending his regimen to anyone, its really pretty severe). He held his diabetes in check for years and years through diet and exercise. Genetics can also play an important role. I certainly didn't fit the stereotype of a type 2 when I was diagnosed, but Im convinced my genetics failed me and I needed chemical help to get my blood sugar under control. 500mg of fortamet twice a day is minimal in terms of diabetic meds and if you watch what you eat and exercise and do all the good things that you should AND are blessed with good genes, well, you may just stay where you are forever.
Oral meds do have a history of failing over time, so the typical type II person would eventually progress to stronger meds. The key is to do everything to protect your beta cell function NOW and you may never get to that point. If you do, however, its still not a big deal as you can increase your meds or even go onto insulin like jeannie and live a long very healthy life!