What if Piccolo killed Frieza?
He had the edge over Frieza second form. Let's say Piccolo doesn't let him transform, and he kills him. He would then kill Vegeta. He told Vegeta he would deal with him after Frieza.
So Frieza and Vegeta are killed. Namek never explodes and Goku doesn't become a Super Saiyan yet. Goku would still be stronger since he did decently against Final Form Frieza, and piccolo got trashed by third form. The power gap would be closer since Goku is not Super Saiyan. He also never learns instant transmission.
Our heroes get to Earth. After sometime, King Cold comes to Earth seeking revenge. Piccolo and Goku trained the entire time since that is what they do.
After an epic battle, all seems lost until Goku transforms into a Super Saiyan. He effortlessly defeats Cold. But, since Trunks is never born, the heroes have no idea about the androids and his heart virus.
Dr. Gero witnessed the battle, and realizes his calculations are wrong about Gokus strength, and gets back to work. Androids 20 and 19 attack. Fortunately in that three year gap, Piccolo and Goku trained because that is just what they do.
Goku battles 19, but his heart virus kicks in, and he is sidelined. 19 and 20 prove to be no match for Piccolo, just like in the regular timeline, except this time Trunks and Bulma do not appear and give Gero a chance to escape. Piccolo finishes off Gero and the androids are seemingly done. Unbeknownst to the heroes, Gero's super computer is hard at work on Cell.
Goku is in agonizing pain and on the brink of death. They quickly gather the Dragon Balls and wish away the virus. Goku is all better. Goku and Chi Chi celebrate and 9 months later Gotten is here.
Flash forward seven years to Buu saga. With Goku being alive those seven years, he is able to keep Gohan and Goten training with the help of Piccolo. They both know that Gohan has the potential to be the most powerful, and that the mantle of being Earths hero will be passed to him and Goten.
Things play out much like they did in the canon timeline. They enter Babidis ship, Piccolo kills Pui Pui, Goku kills Yakon, and Gohan unlocks SS2 against Dabura. Dabura retreats to inform Babidi that evil still lurks inside Piccolo. Piccolo becomes a Maijin.
They return to the tournament, and Goku fights Piccolo, reliving their fight that was so many years ago. Supreme Kai and Gohan fly off to deal with Babidi. Goku being a saiyan, has grown more powerful than Piccolo, but the majin boost(and Goku not wanting to kill Piccolo holds back) makes it an even fight.
Kami appears and tries to appeal to Piccolo, telling him he is not that person anymore. Piccolo tries to fight off his control, but it is not enough. Kami then decides the only way to help Piccolo is to merge with him. Kami's pure goodness drives out the Majin influence, and Piccolo is stronger than ever. Even more powerful than Goku.
(This is where I start running out of ideas)
Meanwhile, Buu is born, and after an epic fight, even SS2 Gohan can't defeat him much like Vegeta in the main timeline. Supreme Kai takes Gohan to train with the Z Sword.
Piccolo and Goku sense Buus energy. Goku realizes he is no match, and tells Goku to use the room of spirit and time to train. Piccolo goes to fight Buu but makes a stop at a kitchen supply store...
Piccolo finds Buu and the two begin to fight. They are evenly matched. Piccolo remarks to Buu that he isn't the only being that has been sealed. Piccolo reveals the rice cooker he picked up. He then performs the Mafuba on Buu, and seals him away.
13 years later Cell is born in Gero's lab. 17 and 18 were never activated, so Cell easily absorbs them becoming Perfect. He goes to show off his Perfect power and is effortlessly trounced by Piccolo, Goku, and Gohan.
The end