Once you decide to bring a gun to coerce others you've decided to use the fear of death to get what you want. That's what using a gun to committ a crime is. Once you put the fear of death into others, they're justified using death to remove that threat.

It doesn't matter if you don't intend to shoot, or if they gun isn't loaded, or if it's a fake gun. The reason you have that gun is to use the fear of death to get what you want.

Now, to your point about him getting caught later, no, I don't believe he deserves to be put to death. If he is no longer threatening anyone with death and did not kill anyone, death is not the appropriate justice. But I do believe if an individual decides to introduce the fear of death, then they are fully deserving if they meet that fate themselves while doing so.