At the moment it looks like they'd struggle in the Championship next season too
I think they will regardless. Unlike Newcastle, it seems Sunderland have always kept wage reductions in the contracts of their players in the event of relegation. With relegation now confirmed, the smartest thing they could do is give opportunities to some of the younger players and limit the amount of time for players who won't be there next season. By the looks of things, even if you take the transfers of Defoe and Pickford out of the question, and the loans for Januzaj, Denayer and Manquillo, there are several first-team players who appear to be out of contract (Pienaar, Anichebe, Lescott, Larsson, Kirchhoff, O'Shea)