1 year earlier...
He kills Z fighters, goes to Gero's lab, absorbs the Androids and fucks up everyone. The end.
1 hour earlier...
Z Fighters feel his ki and go to Ginger to investigate. Cell is stronger than them individually, but he's outnumbered,
so he escapes with Solar Flare. The heroes are still in the dark about Cell's identity. Kami gets worried and decides
to fuse with Piccolo already.
Being the top dog, Kamiccolo is the one to fight 19/20, so they're probably beaten before Gero can activate 17/18.
Then Z Fighters go to Gero's lab just in case and destroy 17/18 before Cell can absorb them.
Goku/Vegeta never see beyond SSJ and, even if they do, they're still too weak to beat Dabura 7 years later.