So sad about the opera :(((

It must feel awful to know that your work has been completely forgotten. Unfortunately, this is the fate of many things related to Sacher-Masoch, even when they were tied to more well remembered characters. An example of this is the opera "Kassya" by Léo Delibes (librette by Henri Meilahac and Pilippe Gille), who you may know for the "Lakmé". "Kassya", the opera, was adapted from "Kassya", a short story by Sacher-Masoch. Delibes didn't manage to finish it since he died in 1891, but the work was continued by Massenet, and finally brought to the stage in 1893, on the 24th of March as for this source.

Unfortunately, there are just two pieces that you can listen to online: the Prelude and a Trepak. There was a performance in 2018 from what I can find, but not much more.

And you can find the mise en scène here