Ok, couple things here. That was actually pretty informative, and I appreciate that. But there are couple things I'm going to have to ask you to clarify. And you seem quite tired of doing that. Oh well.
First. When you cite a source you need to reference where it's from. If it's a web novel just mark down the chapter. If it's a LN a volume and page number. The point being so that I, or anybody else, can look it up.
Second. The snippets of dialogue your quoting there don't actually support what your saying. I don't see anything in there that supports your statements about the nature of Od Laguna and a scope of his dragon sword attack.
Quote 1: Soul of world. Got it.
Qoute 2: People go insane if they see it but take there magic to another level beyond what Od Laguna is cool with. Got it.
Quote 3: Od Laguna is the consciousness that rules over everything in the ReZero world. Got it.
None of this points to destroying it being the same as destroying the universe. Or even that it's exists independently of one planet? The text of the Roswaal quote you said the author confirmed specifically says "world". I don't know how big the ReZero universe is but I'm not sure how to even write a fraction small enough to express what one world would be in the scope of a universe. Just one galaxy can have like 100 billion stars in it.
Is there something that says it extends to all of reality somewhere? I understand that there is some dimensional travel going on or something from somebody since Subaru was Isekai'd and jumps timelines or travels through time. Even if destroying Od Laguna destroys all version of that world it doesn't necessarily destroy the universe. Small ripple in a big pond.
Sidenote but this made me laugh...
Roswaal: “Make sure you don't misunderstand. This possibility is present because it is her. There is no way to bring back lives that have met a conventional death. The Od Laguna would never permit such convenient magic as resurrection.”
That is an impressively ironic statement after discussing Reinhard. Poor Roswaal is in for a shock someday.