To the best of my understanding, (as other have said) there's no medication for did. It's a trauma reaction. The best way to "heal" it is through dealing with the trauma/s that caused the severe dissociation. Meds can address mood and psychotic symptoms, but cannot alleviate the trauma reaction. It's the same with ptsd; there are meds for nightmares, depression, anxiety, and such, but there are no meds that cover it all in one package.
I'm not sure how the naltrexone might work to mediate switching. It works for additions by talking up the receptors the specific drugs would utilize to cause a high. I tried it for self harm at one point (it was really severe and they were grasping at straws). It was supposed to prevent the rush of endorphines from the sh, but it didn't actually help me, so I'm not sure.
Antipsychotics may work to dampen the experience of parts awareness but would do nothing to address the underlying issues. Heavy sedatives may also work similarly diminishing the awareness of parts, but then you'd simply be heavily sedated...