i think medical nin doesn't go so far as to resort soul to ones dead body its not healing.
medical nin heals or restores the body that has taken damage as that's the principle its built on but to restore soul well that's something else i'm afraid.
if it was possible via medical nin well no one...
the question we should be asking is if the 3rd coffin was really minato and if it was did kishi forget that rds had his soul seal or was it a plot hole/inconsistency cause BM 4th if he had that mode at the time would have destroy hiruzen neg diff.
kyuubi couldn't go back to his main because for one he is seal inside minato making him a jin so yea he wasn't a free.
on the other hand where would he go seeing as how his other half is inside naruto and i dont see where biiju just walts inside someones body lol.
lol so its like this minato...
remember orochimara seemed to have figured out a few secrets about the reaper death seal so he probably knew what to do to get his arms back while freeing the hokages.