WARNING: The following contains spoilers for Dragon Ball Super Chapter 63, by Akira Toriyama, Toyotarou, Caleb Cook and Brandon Bovia, available now in English from Viz Media.
After training Goku in the use of Ultra Instinct Sign, Merus intended to accompany the Saiyan to Earth so as to fight Moro and save the universe from destruction. However, Whis intervened, revealing Angels are meant to remain impartial and that Merus would be totally obliterated if he interfered in the fight. While at first Merus watched the battle from afar, the hero finally joined the battle against Moro in Dragon Ball Super Chapter 62. In Chapter 63, Merus and Moro fight, with the former taking out a key ability of the former. However, this fight costs Merus his life.
At the start of Dragon Ball Super Chapter 63, Goku and his fellow Z-Fighters are out of commission after Moro thoroughly devastated them. The energy-absorbing villain had, at a decisive moment in the battle, chosen to go and take a copy of his powers from Seven-Three. This also resulted in Moro getting Seven-Three's ability to copy the powers of others by touching the back of their necks, though Moro wasn't subject to the same time limit as his henchman. This ability also allowed Moro to get access to Vegeta's Spirit Fission, which renders fusion worthless.
After teleporting Goku and the other Z-Fighters away, Merus takes on Moro, buying time for Dende to heal the Saiyan. However, when Goku finally returns to the fray, Ultra Instinct Sign still isn't enough to take down Moro, who is more powerful than ever before. Goku laments his weakness, but Merus reveals the Saiyan will soon be able to tap into a more powerful level of Ultra Instinct. While they're talking, Moro attempts to steal Merus' powers, but the Angel -- who has been hiding his true strength -- cuts off the energy-absorbing villain's arm. Realizing Moro's copy power might give him a major advantage, Merus then proceeds to destroy each and every one of the jewels in which the villain stores his ill-begotten powers.
However, as Merus attacks Moro, he starts to fade from view, which appears to be the total obliteration about which the Grand Priest had spoken earlier in the arc. The hero explains he cannot be impartial and sit back while injustices are occuring. Whis, for his part, seems to have manipulated events so that Merus is even able to fight in the first place, allowing the Angel to choose his own fate and to save Earth by giving Goku the push he needs to jump up power levels. As the chapter ends, though, Merus fades from view, exhorting Goku to protect the galaxy and universe that he has come to love.
While there was some speculation Merus might have gotten some sort of special dispensation to fight Moro, Dragon Ball Super Chapter 63 makes clear the Grand Priest did not approve any interference in this case. As such, Merus really seems to be gone for good, having sacrificed himself to give the universe a more powerful protector. Plus, by taking out Moro's copy ability, Merus has given the Z-Fighters the chance to face the energy-absorbing villain on their own terms.
Dragon Ball Super Chapter 64 releases Sept. 18.