Unseen timeline set-up:
The events up till Freeza arc occur
Future Trunks from Cell's timeline comes to warn the Z-Fighters like in the main timeline
They train for 3 years as planned
Trunks finds a way to defeat the Androids in his future via blueprints
He is not strong enough to defeat Cell and dies
Cell uses the time machine, but ends up in the the History of Trunks timeline as well as the main timeline
Unseen Timeline Events:
The Android saga goes normally except that there is no Cell to interfere
Thus this means that Piccolo fights 17 uninterrupted and they are equal in power
Piccolo possibly kills 17 considering how surprised 17 was when Piccolo unleashed the Light Grenade technique on Cell
Vegeta would have trained in the time chamber regardless of Trunks being there or not
At the time that Vegeta comes to the battlefield, Piccolo may have finished off 17 and 18, otherwise it is Vegeta who offs them
16 is also destroyed by Vegeta
Since Cell isn't present, the world is safe and Trunks is dead so he still doesn't return
Goku most likely enters the RoSaT in order to catch up to Vegeta
No Cell means Goku doesn't die and Gohan doesn't learn SSJ2 or perhaps even SSJ
7 years pass by, Vegeta achieves SSJ2 and so does Goku
Majin Saga begins normally except Gohan doesn't have SSJ and Videl isn't as famous
Tournament occurs but Gohan won't use SSJ against Kibito, but he may achieve it in seeing Videl get beaten by Spopovitch
Gohan still gets drained and then Babidi's spaceship happens
At this point I think Gohan and Krillin get turned to stone
Piccolo fights Pui Pui, Goku fights Yakon, Vegeta fights Dabura and kills him
No Majin Vegeta
Buu isn't released and Babidi is killed as well
BoG: Beerus comes to Earth and there is no Buu to take away pudding so there is no conflict. Goku would still spar against him and lose horribly. Goku probably asks to use the DBs to find out about SSJG and then fights Beerus again.
RoF: Assuming the above happened, then this goes the same except that Gohan is massively weaker here and probably dies.
U6: Buu doesn't exist to be placed in the team and Gohan can't go so really it's Krillin who gets thrown in there. The tournament is unknown at this point, but I think the order of fighters would be Goku, Piccolo, Krillin, Vegeta, Monaka. This changes everything after Frost. Piccolo vs Magetta happens and Piccolo loses from being tired, Krillin vs Magetta happens and probably loses as well. Then everything proceeds as normal.
Potafeu: Goten and Trunks are killed by Copy Vegeta since they don't have the fusion dance. Everything else is normal and the kids get revived.
Zamasu: Well Trunks wouldn't come back to warn them so everyone would be unaware of Black. In fact, Zamasu just watches the GodTube footage of the tournament and decides to switch bodies with Goku and kill him. Then, he goes to Cell's timeline and kills everyone there along with Future Zamasu. The only difference here is that Babidi is still alive in Cell's timeline, but he would be killed by Zamasu anyways along with his whole army. Alternatively, Future Zamasu could be caught off guard and then have his energy drained and given to Buu. It doesn't seem implausible and could bring out a god ki Majin Buu, but that's a whole other story to tackle. What does happen is that both of them finish off U7 and then die in U6 when Hit assassinates Black and then Future Zamasu survives due to immortality, but stands no chance. The rest is unknown, but Zamasu would be contained somehow while Black is dead somewhere.
The unseen timeline continues as Goku and family are restored, but Goku is still in Zamasu's body. The best choice here would be to have Whis or the Supreme Kai to send Goku to the alternate timeline after doing a bit of research. The problem is that U7 would be desolate so they would probably look in U6 next. Goku would get recognized and eventually Future hit would be called to find Black's body. They go back to the unseen timeline and revive and subdue Black in order to switch back the bodies and Zamasu is destroyed.
Interlude and rest of Super: The interlude would occur the same as usual and Super continues whatever.
EoZ: Uub does not exist so the tournament probably ends in Goku and Vegeta fighting or something like that. Around this time is when Cell of the unseen timeline should be completed however.
Present Cell Saga: Cell is finally completed in Dr. Gero's lab and breaks out. Everyone probably dies from this version of Cell considering that the computer and drones would have been collecting data and DNA from the Z-Fighters, Dabura, Beerus, Whis, Champa, Vados, Golden Freeza, and the U6 team sans Frost up until that point. This means that this Cell would be a Saiyan, Earthling, Namekian, Freeza Race, Demon, God, Angel, Other Alien Race hybrid with time skip hax, damage negation hax, god ki, and a massive amount of potential, fighting ability, and more hax.