In Glasslands, Jul speaks about how their society was a much greater space-faring race before they met the Prophets. Now what would happen if the Sangheili never joined or met the Prophets? Surely the Sangheili civilization would have grown stronger. And humanity would have inevitably met up with the Elites eventually.
So what would happen if the Sangheili never joined up with the Prophets? And what would happen when they meet humanity?
Depends on what terms they met…
Knowing humanity (especially the military side) it wouldnt have gone nicely.
Well the fact that they were space faring indicates that there was a prominent scientific community. Even if they still had a warrior base and all members were trained for combat, that didn’t come at the cost of other areas. If we compare the Sangheili-San 'Shyuum war to the human-Covenant war, the Elites were similar to the humans in the sense that they were at a technological disadvantage. The Sangheili refused to tamper with the many Forerunner relics on their planet, unlike the San 'Shyuum who had utilised such technology to further themselves. That’s what sparked their war.
This indicates two things. Had the Elites not met the Prophets, they still would have been far more advanced than us. They were a space-faring race in 938 BCE, we were still using swords and spears. We didn’t even have steam engines. In the then more than 2000 years it has taken us to reach the point we’re at know (over 1500 years in the Halo Universe), the Elites could travel through space. Now, in that time they may have become less obsessed with the preservation of Forerunner artefacts, they may have stopped caring about them at all, societies change. But, if we assume their culture was unchanged in regards to the Forerunners, then their encounter with humanity could have entirely depended on that. If they discovered the human’s status as Reclaimers before hostilities broke out, then they may have worked with or even worshipped the humans. If they weren’t aware of humanity’s status and humanity were careful enough with Forerunner tech then perhaps it would have begun with negotiations. If they came across humanity when humans were researching Forerunner tech then they may have taken issue with this and started a war anyway, leading us to a similar situation as the ones we’ve seen.
I think that the Sangheili would have been far more advanced than they are now technologically if they hadn’t met the San 'Shyuum. By joining the Covenant they were oppressed, they stopped growing as a species, instead reliant on the Shan 'Shyuum to do that for them. If they hadn’t met the Shan 'Shyuum then the Sangheili could possibly be at a technological level rivalling the Forerunners and if, or rather when, they met humanity they may have even created a peace treaty with them or allied with them against any outside threats.
When they met Humanity, it would have either gone very well, or really badly. They would have conquered the Grunts, maybe the Hunters(The war with the Hunters was won by an Elite). So, they might have accepted Humanity into their Empire as an Ally, after a few battles.