Bardock: Cooler ker-plodes Goku's pod as he's leaving Planet Vegeta
Saiyan Saga: Raditz does what Galan said
Saiyan Saga: Vegeta doesn't do that waiting for Goku bullshit so Nappa kills all the fighters and Vegeta kills Goku since no one is there to help him
Namek Saga: Ginyu kills Vegeta and the rest take care of Krillin and Gohan before Goku makes it to Namek. Goku is then destroyed by Frieza
Frieza Saga: Frieza jumps right to his final form and kills Vegeta, Piccolo Gohan, Krillin and Dende. He then pops the planet and leaves before Goku recovers.
Android Saga: Frieza and Cold pop Earth from space
Android Saga: #17 and #18 kill all the Z Fighters during their first encounter. Then #18 decides driving around is dumb and just flies straight to Goku and kill him while he's sick
Cell Saga: Vegeta doesn't fall for Cell's bait and kills him before he becomes perfect.
Cell Saga: Perfect Cell kills Vegeta and Trunks right after beating them.
Cell Saga: Goku doesn't give Cell a senzu and Gohan beats his ass easily
Cell Saga: Perfect Cell kills Gohan straight away and doesn't try to enrage him.