A while ago I reached out to the Chopin Institute in Warsaw and asked for more info and reference and they generously provided me with a highly detailed 3d scan of the death mask.
Thanks to the scan I was able to fix some areas of the face, specially around the chin and forehead.

Sculpted in ZBrush, the color texture was painted in Substance Painter, rendered in Maya with Arnold, used Xgen core for the hair.