That's my guess too. Some people were saying they think it'll be a fake-out death altogether like comic book shows like to do but the head writer apparently just said that it's a real death that the Lazarus Pit won't fix. Also, it seems pretty obvious anyway given Barry straight up said "Sorry I missed the funeral"

Actually, if you go on the Flash's Facebook page, they posted a preview comic prior to this episode's release featuring Gideon saying that same line but with "founding member of the Justice-" at the end of the sentence.