Captain Cadaver probably didn't get the OP.
Nappa watches the fight along with Krillin and Gohan. When Vegeta resorts to Oozaru, he cuts off Nappa's tail before creating the moon, because his pride won't allow him to get any help. After that, two scenarios...
1. Nappa prevents the others from interfrering.
With no one to cut off Vegeta's tail, everybody is killed (even if Yadjirobe manages to catch Vegeta off guard without the others' help, Nappa is still there to help). Vegeta and Nappa go to Namek, where, one way or another, nobody gets the wishes. Freeza's empire continues.
2. Nappa is annoyed that Vegeta cut off his tail and betrays him.
The wounded Vegeta is defeated by the combined forces of Nappa and the others. Then he accompanies Gohan/Krillin to Namek. With Vegeta not being there, the trio has their potential unlocked earlier than in canon and I estimate that, by the time Ginyu Forces arrive, at least Nappa is strong enough to take them. Goku arrives during the battle. When Ginyu arrives, Ginyu Saga happens as in canon with Nappa playing Vegeta's role.
At Freeza Saga, Nappa isn't smart enough to come up with Vegeta's idea (Krillin wounding him, then Dende healing him) and, if he does, he ends up nowhere near as strong as Getes. By the time Goku has emerged from the healing chamber, Freeza has killed everyone, so Goku dies too, since nobody is there to distract Freeza for Goku to prepare the spirit bomb.
Supposing the others' deaths cause Goku to go SSJ right away, Goku defeats Freeza the same way as in canon, escapes to Yardrat and later returns to Earth. Soon after he has defeated Mecha Freeza/King Cold, Alternate Bulma appears and warns Goku about Androids. 3 years later, Goku fights Nineteen/Twenty alone and dies.
7 years later, Gero is majinized by Babidi and Buu awakens. No DBS.