This story dates back to the late 70's, early 80's. It was in an anthology of award-winning short stories. (Perhaps edited by Lester delRay?) The story line is about a super-star actor famous for his ability to 'become the part'. He not only acts the part, his facial features & body image transforms(which most attribute to his a Ex: One role was that of a skid-row drunk, which he portrayed perfectly after months of wearing filthy old clothes & drinking himself into a stupor for weeks on end. Another was his rendition of a mental patient. For that story he had himself admitted to a facility for the mentally ill & submitted to strait jackets & other restraints.
His 'secret'is revealed when the actor is accused of murder. He'd won the role of a serial killer & in his pursuit of learning how it felt to actually kill another took the life of a young woman. He was identified by several witnesses who recognized the actor. The plot twist comes after his arrest. The actor begins regressing through his stage & film roles & triumphs, playing each part in reverse order.
Several months later the reader finds out no one could communicate with him except by going along with whatever role he was currently re-enacting. He's been put into a mental hospital where he continues to regress. One evening the prosecutor is told to rush to the hospital where he's met by the doctor in charge, who's clearly shaken. He warns the prosecutor what he's about to see is horrifying. The actor, having regressed all the way back to his first part is turned towards the back wall, utterly still & silent.
When the acotr turns around,having run out of parts the detective steps back, horrified & sick, for the man has no face.