No. It will not work. Strontium reacts with water at approximately the same level as lithium/sodium. In an aqueous solution, you will not be able to isolate the metal. Also, magnesium will not reduce the Sr2+ ion back to the metal as it is not nearly reactive enough. Reactivity, in terms of metal displacement, increases as you move down and to the left. So Sr is much more reactive than Mg. Strontium can replace magnesium, but not vice-versa.