Future Trunks lived in a very bleak future and was backed into a corner with Gohan's death and his super saiyanSuper Saiyan transformation not being strong enough to stop Android's 17 and 18.
So So in comes the time machine to go back and save Goku from dying from a heart virus.
When Trunks travelled backwards through time, he creatingcreated a branching time-line. Let's call the present world, World A (where Trunks pwns Mecha-FreezaFrieza)
and and the other world World B (Androids wrecking s***). Now nothing Trunks does in either world affects the other because they are two seperateseparate time-lines.
It was mentioned in superSuper that anytime time is travelled reversely, a time-ring is born to give representation of a new universe being created.
Now in DBS, Buu was never revived in World B because Trunks killed Babidi and Dabura due to a power buff he got from training with Supreme Kai and Kibito with the Z-Sword. However, it is revealed in the manga that the battle with Dabura took a heavy downturn, as not only did the Z-Sword get turned to stone and obliterated (eg. Grandpa Supreme Kai sealed within it was killed).,
But the but Dabura killed Kibito
And and Babidi killed Supreme Kai.
We already know that no supreme kaiSupreme Kai = no god of destruction aka no beerusBeerus because their existence is a set. Which also equates to no Whis because Whis is an angel that exists solely to serve the god of destruction. This also means that the potara fusionPotara Fusion and elder kaiElder Kai unlock ability are non-existent in World B.
So looking at the Gowasu in World B, it was shown in the anime that he was murdered by Zamasu who took a time-ring and collected the super dragon ballsSuper Dragon Balls and wished for Goku's body.
With that time-ring he went to the past of worldWorld B.
Because Black did reverse travel like Trunks, he made a new time-line. In this worldWorld C he was still plain old Zamasu but was planning to kill Gowasu as he had just sparred with Goku.
Black killed Gowasu for a second time and influenced his past self to join him. This worldWorld B past tense Zamasu collected the super dragon balls,Super Dragon Balls and wished for an immortal body. With that Immortal, immortal Zamasu got a new time ring from Black's reversal which allowed them both to go back to World B and kill all the gods of each universe in that timeline.
So Beerus found out, got mad, and killed Zamasu in worldWorld A. That means nothing for two reasons,: first, Beerus' actions do not matter in this world because Trunks already seperatedseparated the timelines way back in Dragon Ball Z. SecondZ; second, even if by some stretch of imagination God's affected the time-line differently. It, it does not matter because of the power of time ring.
- What happened to universe C?
- What happened to earthEarth in universe C, since? Since in that case there would be 2 Trunks (I have no idea what the plural of Trunks is.).
- Why was there like 5 time rings in the episode that Gowasu revealed them,? Trunks has not jumped back and forth 5 times. Or has he? Also, what's the difference between a green ring and a white ring?
NOTE: This is why when anime delves into multi-verse, time-travel stuff, it always turns out bad unless it's stein's gateSteins;Gate. <3
EDIT: Episode 67 of Super reveals why there are so many time rings. The answer is: 2 for Trunks, 1 for cellCell, 1 for blackBlack, 1 for beerusBeerus, and 1 for whisWhis = 6 time rings as shown below.