reread this part and so forth, then you'll know it http://www.mangago.zone/read-manga/kokou_no_hito/an/v17/c170/pg-14/
it explained from there how he got down from the mountain
Buntarou is unable to save his kohai Takemura, who dies in an accident. He is painstakingly able to achieve his lifelong dream of summiting K2 solo, but he loses several fingers and toes as a result of his recklessness. Despite that, he survives, miraculously finding a fixed rope left behind by a prior summiting team, and is able to make it back to his family. The final chapter shows him smiling while thinking of Rokka and Hana, signalling his growth; he doesn't need to go back to mountains anymore, because he's found a place where he can belong.
In the end did he survive and return to his family and now they're having another child, I kind of saw it that way but I'm kind of confused. Is what I wrote correct, someone please confirm Σ(  ̄□ ̄||)