Actually am pretty sure the reaper could have sealed the whole fox if Minato wanted him to. Minato wanted to seal the other half in Naruto do he only sealed half.
@OP Even if their souls are released from the reaper's belly, they won't come back to life.
he didnt "want" to seal it in naruto, he had to because he could only contain half and with kushina already dying, baby naruto was the only other option. Had he not sealed the other half, it would have reformed and continued to rampage and maybe been controlled, maybe not.
OP...assuming kuramas chakra was exactly 1/10 the 10 tailed beast, it would take 20 people using it, and i doubt there are that many people alive in narutoverse who could use RDS. Also they would all need solid chakra pools, it wouldnt allow a random fodder ninja to seal 1/20th its chakra because he couldnt contain it long enough to seal himself. The ONLY slight chance would be a full health nagato could MAYBE seal it or at least most of it himself due to his chakra pool. While naruto has alot, you must remember probably 75% of his overall chakra had always been siphoned off of kurama even when he was a kid, given the unique seal minato used. I doubt using kuramas chakra to seal the 10 tails would work, otherwise you could seal the 10tails in the 10 tails inception style and RDS it with no deaths.