Conservation of angular momentum means that the sphere will continue to spin forever. In order to change the angular momentum you need to apply an external torque.
Note that this treats the sphere as a rigid body. If you consider just a small part of the sphere there are forces acting on it in such a way that the sphere remains undeformed. On a microscopic level these forces would come for example from bonds between the atoms in the small part and atoms in the rest of the sphere. These forces make that part accelerate so that it keeps up with the rotation. However, in the absence of external forces on the sphere there will be no change in the momentum of the center of mass of the sphere, or in the angular momentum.
If the sphere is no completely rigid the angular momentum can in principle be absorbed by internal degrees of freedom, so that the sphere stops spinning.