Oooh, that is -- actually quite difficult! Pre-John Sherlock probably uses the Ring to make people appreciate and understand him, and it consumes him; post-John Sherlock does his damn best to destroy the Ring, not because he viscerally understands that it needs to be done but because John says so and he knows that John understands this matter much better than he does. I think we might end up with a situation where it comes to the point of casting it into the fire and Sherlock can't make himself let go, but he'd cast himself in instead. I expect that at this point John would knock him over the head and chuck the Ring in, because John's good at last-minute saves like that. And then they go home in time for tea!