Honestly, I don't see it being that hard turning Ryback face. He was well over as a face when he turned on Cena after Wrestlemania which looked like Ryback being the anti-hero badass face we've wanted for a while, but they instead opted to use that to turn him heel. Still to this day don't understand that damn logic.
It was a pretty shitty idea, I agree. His face run, regardless of his PPV track record, was working. The pop he got from that Elimination Chamber crowd when Cena hot tagged him in was huge. However, I don't personally think the heel turn killed him. I think humanizing his character did.
Before the heel turn his character literally was a Cyborg. An intense as fuck Cyborg. The Cena feud turned him into a bitchy house wife-borg, though. And then he became a Vickie Guerrero-hugging locker room Bully-borg somehow. It completely ruined everything that they had going for him.
I can really imagine a caveman sounding, jobber dominatin', emotionless heel Ryback working. I can ESPECIALLY see it working with a manager like Paul Heyman. But sadly that boat is passed, oh well.