In his defence, I doubt even Darius expected his form to fall off this much and this quickly. He came in to the season talking about how good he felt and how fit he was, now within 2 months people are begging him to retire, it's gotta be a lot to take in.
I'd say the most realistic scenario with Darius is he gets the remainder of this season at Fullback regardless of form, he'll also get the start of next season (If he chooses to go around again), but I'd say the hammer will drop if he's displaying similar tendencies early next season as he is this season, and Seibold will give him the tap.