Thanks for reading! :) I read up on the lore, and it's implied that the entire raid was an ambush by Omnigul when they went into the Temple by siphoning off their Light to reawaken Crota. They never made it to Crota because most of them died in the very beginning: Vell, Omar, ect. And then Sai was killed by Omnigul's thralls. Toland disappeared. Eriana sacrificed herself for some unknown reason. At least, this is what I'm speculating on based on grimoire cards. I'm heading off to work so can't cite sources now, but thanks!