However, the Zamasu who had succeeded in the original present timeline was still alive thanks to the Time Ring and carried on, eventually learning of his past self's death from Goku and Vegeta in their first trip to the future in the manga.

How was Zamasu still alive in the future?

The explanation was the Ring of Time allowed him to exist independent of the past him who was killed by Beerus. Black explained that he was infact the Zamasu who fought Goku, and that is what made him take Goku's body.

How did Zamasu get revived?

The character debuted back in Dragon Ball Super as the major antagonist of the 'Future Trunks' arc. The story ended with Fused Zamasu being destroyed by Zeno who wiped out the baddie's reality. ... So far, there is no word on how Fused Zamasu came back to life after having his basic existence wiped by Zeno.