No buccal sulcus after closure of OAC: advice?

Authors

A friend's dad. A few upper teeth were extracted last year due to failing bridges, but both sides ended up with significant oro-antral perforation and chronic fistulous tract. Since then, he has been treated by GDP and an oral surgeon. Big buccal advancement flaps were raised on both sides to close the mouth-sinus holes. Both sides are healing well now and the pt came to me for a restorative solution. Upon examination, significant bone loss was noted. No buccal sulcus at all. the mucogingival junction, as you can see on the study model, is too palatal to the crest ridge due to big buccal flaps. Any advice on how to restore this case?