Inuyasha: The Final Act Episode 6

A few problems with your theory.. 1 is that Tenseiga can only bring back the people on the verge of death as in dying not dead.. 2 is that the tunnel that Tenseiga opens is a one way track it sends the soul and body of whoever it slashes to the other world.. Not the other way around... 3 There is no way for him to access the world of the dead unless he himself is dead.. Of course there is that one exception the 2 guards on the volcano but if you havent seen the original that you would know that way was closed long ago.. The other option is to use the gate inside Inuyashas left eye but as we all know that was destroyed long ago.. 4: there would be no reason to bring back Kagura she has served her purpose in this anime.. And Kohaku probably wont die since after all he is one of the main characters sibling..