I don't think he'd make any bold moves like Chaozu, Tenshithands or Big Green, so he'd most likely end up like Kuririn; heavily injured, but surviving. He'd go with the others to Namek, though would mostly be resigned to protecting Bulma until Vegeta took their Dragon Ball, at which point he'd go with Gohan to get his potential unleashed and fight the Ginyus. However, he'd just get oneshotted by Reacoom like Kuririn did and saved once Galu arrived. Against 23k Ginyu, he may be the one to deal the most damage until Vegeta intervenes, given he may channel forth the memories of how he was initially Goku's enemy to motivate him to become Yamcha of the Desert for a short time, though he'd still need Vegeta to intervene. Afterwards, he wouldn't play much role in the fight with Freeza. Most he'd do is die and be revived by the 3rd wish from the Namekian Dragon Balls.
After that, nothing really changes with the plot other than that the potential unlock would make Yamcha far stronger than his canon self, being only a step behind Kuririn, whereas Ten and Chaozu staying on Kaio's for 130 less days would make Tenshithands far weaker than in canon unless he chooses to wait until he and Chaozu are revived together. Either way, it means that for a short time, Yamcha is the 2nd strongest human and may continue to be so in the Cell Arc as well.
So....a small win for Yamcha I guess?