I'm wondering, having a human model made in blender, how can you make it so that at some point (when the human "dies") the body follows the rag doll physics in OpenGL? I tried looking for some tutorials but I can't found one that fits my requests. Specifically how do you make rag doll physics in OpenGl (and if needed using Blender)?
Look into Bullet Physics.
It's a good free library for 3D physics, and the demo code it ships with all uses OpenGL. Not that the physics and graphics API have anything to do with each other, but it might help you grasp the relationship to see code youre familiar with.