A friend tells me type 2 diabetes can be managed without insulin, is that true? even with readings of 300 and sedentary life?

In some cases yes, in others no. T2DM occurs when you can make some insulin but not enough to keep your blood sugars in a desired range (70-100). When they remain in the 300 range tissue damage to eyes/kidneys and other sites will eventually blind you & make your kidneys fail. Adding insulin to treatment is necessary in some but not all patients.