And I will offer the hand of Welcome... Yes I have lost my mind and a few friends by looking up with a little giggle They just have no idea or, if they do. Do not care.
I do not know where your view of the sky is from and if you can access a telescope or not. Getting away from city light pollution can only enrich your experiences.
Your question is interesting and impossible to be absolute about. We can 'see' 13.7 billion light years. They say. So any Gamma ray bursts that we see has happened closer to us than that. According to me. What reaches us is just the smallest fraction of the energy that was ejected... how far it goes would be dependant on the not being stopped by any thing in the path. Space would be accurately described as empty. Empty does not make it devoid of all matter.
The Gamma Ray Burst might have been born from a star collapse or destruction of the same as it entered or became a Black Hole. I am very pleased this does not happen often around here. When you ask ' What is left ?' Do you mean as its destination furthest point. Or at that SMBH starting point. And my answers would be...a almost unmeasurable blip in the back ground tempreture of space... or a SMBH.