In the Stern Gerlach experiment, when does the electron's position get determined? Before/right after it leaves the inhomogeneous field? Or when it hits the detecting foil? This could be tested by replacing the foil with two slits at each of the expected regions of electron incidence. If there is a diffraction pattern on the other side of the slits, that means that the electron was in a superposition of spin up and spin down states after leaving the inhomogeneous field.