If you say that someone is a goner, you mean that they are about to die, or are in such danger that nobody can save them. She fell so heavily I thought she was a goner. be a goner if someone is a goner, they are soon going to die, to fall, be caught etc (gone)
a person in desperate straits; someone doomed; "I'm a goner if this plan doesn't work"; "one mistake and you're toast