Nappa coming to Earth instead of Raditz?

[SIAD]

Suppose Nappa goes to Earth first and Raditz accompanies Vegeta.

How would the story unfold?

 

[Captain Cadaver]

The tail strategy wouldn't work and Nappa would be far less merciful than Raditz, meaning he wipes out all life on Earth long before the other two arrive. Maybe Gero could survive at first by holding himself up behind his Katchin Gate, but he'd either have to do such a rushed job with the Artificial Humans that they wouldn't reach Freeza's level or he'd eventually die of starvation.

Short answer - Freeza remains unopposed unless he runs into Babidi or sends some scouts to Vampa.