Kabr, a Titan, was corrupted by the Vex. He went mad from the Vex effects and the realization he did not remember an entire fireteam. He used the hammered chassis of a Gorgon and his own Light to create the Aegis. Praedyth, a Warlock, succumbed to the Oracles, becoming stuck in a time loop. He remains in the Vault, and we will possibly see/rescue him in the Unsealed Paradox mission. Pahanin, a Hunter, was probably not on Kabr's original fireteam. However, he did witness Kabr's fall, both to insanity and the Vex. He remembered some of the last words Kabr said to him, but became frightened of traveling alone, creating the Super Good Advice to keep him company. Osiris, a Warlock, was the one who inspired Kabr's trek into the Vault. I do not think he ever ventured into the Vault itself, or he would have shared the info with the City (and been banished earlier).