I came to this thread specifically to point this rule out. It's been made apparent time and again throughout the arc that if an angel breaks that one law, they're erased. It's the only way to truly get rid of an angel.
This would be a complete rigmarole of a way to beat Moro, but maybe that's Goku's goal. Moro's been alive for for more than 10 Million years and he's been locked up ever since. So the idea of him going back in prison willingly is absolutely out of the question. He hasn't let go of that grudge all this time, why would he now?
They've also made it a point to say that 7-3's copy abilities aren't just mere mimicry -- they're quite literally YOUR abilities, so it's just as if YOU were to execute the techniques. So if he's absorbed Merus somehow, that would mean he's also an angel now too by proxy, especially since there's no time limit. If that's the case, theoretically all Moro would have to do is seriously try to kill Goku and he'd get himself Thanos'd. Whether that will happen though... who knows. It's hard to say if Goku is actually thinking that far ahead.
If not, the only other solution is to get Vegeta all restored and get him to do the Forced Spirit Fission again and this time actually finish the job since there shouldn't be any escape routes left for Moro after that. 7-3 being absorbed makes sense because Moro had said since the beginning that he was keeping him around for a certain reason, and Shimorekka is killed now. Let Goku in MUI distract Moro while Vegeta can land some damage and slowly get Moro's energy drained, and then wrap it up. Cause I don't know how Goku is going to beat Moro otherwise via brute strength.
MUI with Jiren is one thing, but Goku's borrowing power that the angels do naturally. I don't think he's even
remotely ready to tangle with angels yet, never mind seeing just how he measures up against Beerus.
Also, I can't help but feel that with Vegeta's character development in this arc... I wonder if the story will shift to where HE becomes the hero people rely on now, because Goku absolutely blew it. They've been making it a point to talk about how he's been wanting to atone for his sins, especially with the Namekians, and while Goku was getting dusted, everyone was waiting on him to come in and save the day. It's like what someone said in here already, there has to be some sort of consequence for Goku's recklessness and I hope Whis and Beerus call him out on it. But maybe that flashback with Merus was a clue -- Goku's never been a hero of justice, he says it himself, the strongest guys he wants to fight usually tends to be villains, so that's how that kinda works out.
But with Merus getting erased and possibly absorbed... The Grand Priest is going to be pissed. Goku's going to have to answer to all of that as well, even though that's not really Goku's fault himself, Merus willingly sacrificed himself. Idunno, I could definitely see some angles where they could take the story next, but I really hope Goku faces criticism for his actions in this arc. An angel was absorbed by a villain, and even though they're not supposed to take sides, there's absolutely no way the Grand Priest isn't going to step in. That's a
huge deal.