yes, sneary. it's like any wound, it will grow back but takes time. first the tissue will grow back, then the patterning (though it might be a little off from previous appearance). it takes quite a while to regrow i've found. mine has been regrowing her disc for about 2 months now and is not completed, but you can definitely tell she's getting there. just divide them, plenty of clean water, and give her time.
i used eggcrate to section the tank in half, so that way they still have room. try doing this with eggcrate cut to near tank width and height, and use suction cups to keep it up. it will give her more room than your 65 gal sump will, she can still see/interact with the other ray through the eggcrate, they just can't really get at each other. i find they stay social if you do it this way.
i agree mshill, mela/pimafix are both worthless. waste of money and provide no benefits other than green tea smelling water.