Board Thread:Speculation House/@comment-39854843-20190731084207/@comment-44499733-20191124203033

Ruby: "Her... last mission... was that another Oz's secret?"

Qrow: "There was a lot of those back in our day, but this one was a Summer's secret. When she didn't come back, Ozpin is in the dark as myself and your father. Still, who knows what he may've hidden from us over the years."

- RWBY Volume 7, Episode 4 (13:05)

This seems like no one knows if Summer died or not. All we know is that Summer Rose was Missing In Action. Not even Ozpin or Qrow knows what happen to Summer.