Hi! I dont know how long ago this was posted or if you still need help but i can point you in the right direction, Gus was afraid of oblivion because he was afraid of being forgotten. He was afraid that he would never make a lasting impact and would someday be completely forgotten. Oblivion can be defined as the state of being forgotten. He is not necessarily afraid of losing his body or that there isn’t anything after death, rather he’s afraid that nobody will remember him after he has passed which makes him desperate to do something “great” during his life. This is similar to what many people experience simply because it is something that thousands if not millions of people fear it, its extremely common. I hope this helped!