So, I ended up to where I would lose Greirats questline if I fought Yhorm because I had already killed Aldritch and he still needed to go to irithyll. THING IS: I had already exhausted Dialogue with Siegward at the kitchen, so he would save greirat if I killed a boss. Old Demon is usally my go-to for this exact questline point, but I had already killed him, as well as all the other optional bosses. Yhorm was my only choice but that means losing greirat for nothing.
SO I went and killed the Dancer. Greirat gets saved by onion, I immediatly send him to Lothric, and then I figure screw it I'll go cheese ocieros too. I get back, go save siegward from his cell (Karla too) but upon going to firelink, leveling up, then returning and going to Yhorm, Siegward does NOT appear.
Am I missing something? (Will check back for responses)