It all starts with Trunks in the Android saga
Future Trunks lived in a very bleak future and was backed into a corner with Gohan's death and his super saiyan transformation not being strong enough to stop Android's 17 and 18. 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 creating a branching time-line. Let's call the present world, World A (where Trunks pwns Mecha-Freeza) and the other world World B(Androids wrecking s***). Now nothing Trunks does in either world affects the other because they are two seperate time-lines.
Because Trunks committed two actions the separation was made. He intervened in the past by killing King cold, Freeza, their henchman, and saving goku. And he broke the taboo by going backwards.
It was mentioned in super that anytime time is travelled reversely a time-ring is born to give representation of a new universe being created.
Fast Forward to the super worlds
Now in DBS Buu was never revived in World B because Trunks killed Babidi and Dabura. However it is revealed in the manga that Dabura killed Supreme Kai and Kibito as well. The Androids were wreckt by Trunks when he returned to his own timeline.
We already know that no supreme kai = no god of destruction aka no beerus 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.
So looking at Gowasu in World B, murdered by Zamasu who took a time-ring and wished for Goku's body. With that time-ring he went to the past and intervened by killing gowasu again and talking to his past self.
This is where things get icky
Because Black did the same two things Trunks did (reverse travel, and intervention) the world he went to caused a split into a world C. In world C he was still plain old Zamasu but was planning to kill Gowasu as he had just sparred with Goku.
Black killed gowasu instead and gave Zamasu the time ring that was made there. Then they went back to World B. Killed the gods of all the universes in world B and destroyed the super dragon balls in world B after Zamasu wished for immortality.
The real kick in the chops
So Beerus found out got mad killed Zamasu in world A. That means nothing for two reasons, first Beerus' actions do not matter in this world because Trunks already seperated the timelines way back in Dragon Ball Z. Second even if by some stretch of imagination God's affected the time-line differently. It does not matter because of the power of time ring.
THE PLOTHOLES HERE ARE GAPPING ONES
- What happened to universe C?
- What happened to earth in universe C, since in that case there would be 2 Trunks(I have no idea what the plural of Trunks is.)
- Why was there like 4 time rings in the episode that Gowasu revealed them?
NOTE: This is why when anime delves into multi-verse, time-travel stuff it always turns out bad unless it's stein's gate. <3
EDIT: Mostly done, still need to do a grammar check and post screenshots from the anime and manga to back up my arguement. ETA tommorow