It can be stopped, and it can be polished out.
Polishing the pits out is the best option.
You can send it back to S&W to have it done, you can send it to a top gun refinisher service like APW/Cogan or Ford's, or you can do it yourself.
The best options are S&W or one of the refinishers. They can do it fast with no mistakes.
If you attempt it yourself, use wet or dry abrasive cloth wrapped around a wood block to keep the frame surface perfectly flat and even with no dishing it out or rounding it off.
Polish with a back and forth motion and inspect the surface often to make sure you're not tilting the block and rounding the flats off.
Once the pits are gone, switch to finer grits of abrasive to restore the factory finish. Since the grip frame is covered you don't need to do much past polishing the pits out.
To prevent rust in the future, get Johnson's Paste Wax or the very high grade Renaissance Hard Carnuba Museum wax. NO CAR WAX.
Apply a medium thick coat to the frame where the grips cover it and let it dry 30 minutes. Don't wipe the wax off.
Reinstall the grips.
The wax will protect the metal from moisture and sweat that leaks under the grips.
If the grips are wood you can also apply a coat of wax on the inside of them too, but don't apply wax to rubber grips.