You beat me to it. I have always wondered why Ginyu left Goku around after taking his body.
I was going to ponder it for a while before opening this thread, but i might as well try to
come up with stuff as i type.
First of all, would Ginyu inform the Z fighters that he killed Goku? Knowing him, i'm pretty
sure he wouldn't be able to resist telling them. This would cause Gohan's rage, so he'd rise
to the level that shook Freeza's 2nd form and he would kill Ginyu, without giving him any
time to react or attempt body switch again.
After seeing Gohan's rage, Vegeta wouldn't dare interfrering with the wishes, so the
third wish would have been used to revive Goku. Freeza shows up almost right next
moment. Piccolo hasn't arrived yet.
So, how does the fight go? It depends on how willing Goku would be to let Freeza
transform. Knowing him, after fighting Freeza's 1st form with 5x or 6x kaioken for
a while, and after Freeza declares he can transform, Goku goes like ''YAAY, stronger
opponent, go for it''. Of course, Krillin will try to convince his ally to finish off Freeza
without allowing him to transform, but to no avail.
10x Kaioken Goku and Initial 2nd Form Freeza fight evenly for a while, until Freeza
powers up and stomps Goku. Gohan goes mad again and attacks Freeza (Piccolo
arrives at around this point). This gives Dende time to heal Goku (zenkai).
Piccolo interfreres to help Gohan and takes over. Eventually, Freeza transforms
again and stomps Piccolo. Goku takes over. This time, he's pissed and he overkills
Freeza before he can reach his final form. Everything goes back to normal.
Trunks comes from the future, shows them his SSJ (so that they train to reach it)
and warns them about Androids. Vegeta has one less zenkai, so he becomes SSJ a
little later than in the series, but that doesn't make any essential difference.
Androids Saga goes as we know it, up to the point Cell shows up where Piccolo and
Seventeen are fighting. Goku cannot save Piccolo and Tenshinhan, because he
doesn't know Instant Transmission. Piccolo and Tien are killed, but, since they're
non factors at this point, Cell Games go as we know. Cell blows up the planet,
since Goku cannot save them with Instant Transmission. Super Perfect Cell goes
to explore the universe.