Green’s Dictionary of Slang

1. gone, absent.

1974

G.V. Higgins Cogan’s Trade (1975) 45: So I say, well, it can wait, we make it again, right? And we do. And then, after, I’m gonzo.

2. (also gonzo alonzo) finished, defeated, useless; of a person, doomed.

1987		G.W. Clemente Cops are Robbers 75: ‘Three guys came up to my club [...] and took me for a ride. They put a fucking hood over my head [...] I thought I was finished, gonzo’.
1987		M. McAlary Buddy Boys 88: I don’t know if they gave him money the second time or just took him for a ride. He was gonzo alonzo [gone] after that.
1999–2000		Guardian Guide 18 Dec.– 3 Jan. 170: It’s so thin and weightless that by the time you eat it, it’s gonzo.

3. (US) drunk.

1980		Eble Campus Sl. Spring 3: gonzo – very drunk.
1989		M. Belmonte Computer Science and Why (1993) 🌐 These people are [...] gone, gonzo, gonged.
1996		Eble Sl. and Sociability 77: Gonzo ‘insane, wild’ becomes one of the many synonyms for ‘drunk’ in college slang.