seriously you guys need to stop making up things as you want.
We don't know what happened to the lunari,we don't know if they were betrayed and slaughtered,they could have been just as good been destroyed by a giant meteor or tried to attack the solari and were killed in self defense.
Actually I was looking into this. I believe they were killed off within the last 100 years. Nami's lore says that her people require a MOONSTONE every 100 years to survive. A chosen marai was to find an abyssal pearl, come up to the surface and trade with the bearer of the moonstone for the abyssal pearl. I wonder who could have traded with them? It's obvious it was the Lunari. No one else has any correlation with the Moon. This tells me the Lunari were benevolent because they cared enough to keep another race alive even though they did not need to. They could have left them to die but, they didn't. Now another moonstone is needed which means their 100 year period Is almost up. Why would a benevolent people attack someone? Why is their lack of any evidence of their existence. Even if a natural disaster happened many artifacts and things of such nature would still exist. The Solari killed them because they were evil? No, because of what I said above about them bebeing benevolent and caring enough to keep the Marai alive when it was not required of them. I don't exactly know the life span of Runeterra's people, they could only live up as far as their 50s without magic for all we know. So what was found could in a way be considered ancient to them. It's unfathomably unlikely they were killed by so outside force. Rakkorians are the greatest warriors in runeterra they only fight when outnumbered 10 to 1 or more, they have never lost a battle. It would be absolute suicide to try and invade them. No it can only be an inside job. I don't like assuming but, this one of the few logical conclusions I can come to.
Although I can't quite disprove that the Darkin did not have a hand in it. Aatrox would basically make people insane and thirst for blood and violence. So it's possible the Solari are still responsible for killing them but it may not be by their own accord in a sense.
Thi may be the wrong place to debate this.