Do you think Achilles would have been in the wrong if Odysseus, Pheonix, and Ajax hadn’t made their embassy? They did, so he was. He wasn’t really in the wrong before then, so it stands reasonable that he wouldn’t have been in the wrong if they’d never gone to carry Agamemnon’s apology.
But that also feels like a moment-in-time thing. Taking the Iliad for the time period that it was gives the morality that the story follows. Now, in these modern times with modern moralities, I’m not sure Achilles wasn’t wrong all along. Maybe his error didn’t come to the fore until the embassy, and for dramatic purposes it wasn’t visible. But perhaps he was still wrong to abstain from the combat.
I don’t know. That has a lot of laudable warfare in it, something I find questionable in a circumstance like the Achaeans’s. Wondering about questions like that strikes me as being similar to arguments about the Heisenberg Compensator from Star Trek.