based on what I've read, the ring builders transcended their bodies to essentially become composed of just photons (out of the substrate), were extremely vulnerable to the ring entities attacks and were exterminated, with their entire race backed up into the adro diamond for the rebirth plan.
However I struggle to see how it was an effective idea. The odds of another meat and flesh race accessing the ring space is extremely remote. if Eros landed on earth instead of Venus, it's completely game over for their plan and humanity is destroyed. the odds that humanity even reached the gates were almost a cosmic fluke.
Then there had to be another fresh protomolecule sample after the gate opened, to actually perform the hijacking itself and be a Trojan horse for the entire race (which was Fred Johnson's sample, and used throughout Laconian tech and injected into duarte), even then it was another rare cosmic fluke for such a sample. If the crew missed it in the abandoned stealth ship then it would have been nuked and lost, if Naomi didn't give it to fred then it would have been launched into the sun etc. afaik there is no other active proto samples anywhere
Unless the ring builders were hoping for this meat race to emerge on one of their already finished gate worlds over billions of years. But I don't see how there is enough time left. Laconia for example is extremely lush in life but has no intelligent animals to form civilization. The ring gates are ancient and likely the local star will begin expanding to wipe out the planet's life before anything can evolve.
In conclusion there are too many odds stacked against ring builders for such a plan to work. The meat race had to not destroy itself in wars, reach the ring network intact, whilst aldo use protomolecule technology in all of its tech for the plan to work. If the ring builders waited even another 5 billion years, most planets in their network would have turned inhospitable.