How this civil war ends will bring no change into the Water Tribe´s line of succession. If Unalaq remais chief, his children are his heirs. If Tonraq is the chief, his heir is Korra, since he did not father more children. And Korra cant be head of state because she is the avatar. The chiefhood passes to Eska+Desna. They can rule together, spit up and one keeps the north and the other the south or the eldest rule only one side of the tribe.