Just for who would encounter the same problem, after you try to use the nvidia driver, 3D (direct rendering) is unavailable, even with the intel driver, if you have the nvidia driver installed, because the x server tries to load the nvidia opengl library. If you uninstall the nvidia driver, the mesa opengl library becomes available again and you have at least some 3D support.
I tested with 260.19.21 too, same problem.
Just for who would encounter the same problem, after you try to use the nvidia driver, 3D (direct rendering) is unavailable, even with the intel driver, if you have the nvidia driver installed, because the x server tries to load the nvidia opengl library. If you uninstall the nvidia driver, the mesa opengl library becomes available again and you have at least some 3D support.