Board Thread:Versus Debates/@comment-31337598-20180202202814/@comment-9782468-20180205015939

Lorenzo.r.2nd wrote: a defeat is when u win. minato didn't win. he had to die. its totally different from kaguya's case. there was no sacrifice, or "terms" to be followed. Minato could have sealed the entirety of Kurama again without killing himself, by sealing Kurama back into Kushina and letting Kushina die. But that would have tipped the power balance away from Konoha.

So he decided to seal him in Naruto. However, he couldn't seal all of Kurama into Naruto solely because Naruto's body was too small (Kushina already said he could seal Kurama back into her, and Minato himself stated Naruto was too small at the time to house all of the chakra).

So he used the reaper death seal to seal half of Kurama into himself before sealing the rest into Naruto.

TL;DR Minato could have sealed him all without dying if he wanted to. The reason he didn't is because he was looking out for Konoha's future.