Discovered under the plaster painting on wood ~ 18 century. Renew or rewrite?

[Terehov]

In a private apartment in an old house , the repair took off the plaster from the ceiling . The room and hallway . Obduli air . Found a painting on wood .
The customer wants to restore it.
My thoughts on this subject ..
Refurbish or restore the lost art pieces and coat acrylic lacquer ?
But beautiful it is and how to live with such a ceiling ?
Or completely restore and paint a tree and write new colors ? In this case, an old painting would be lost . but it will look more careful ?