Only Robert Can Do This

That has to be good news! 

Indeed.  Robert is still alive, but he cannot move.  He can feel the excruciating pain caused by the explosion. 

He planned on doing this because he knows he is the only person here who is immortal and has the ability to not die. 

But in all honesty, he is not sure what will happen by using himself to get Diablo to detonate the bombs right there.  Even if he is immortal, he never tried bombing himself.  He did not know if he could survive the explosion.

Fortunately, in the last second, Jack took Robert away from the center of the explosion, decreasing the deadly impact on Robert's body.

And then, Rosanne's tears have got the severity of the injury under control and begun the process of healing. 

Therefore, Robert has not become a dead man, with his soul wandering in front of Jack.