Alright then. Lets assume that you don't have backups or the ability to restore the file to a previous state. so it may be the unfortunate case that this workspace is truly corrupted and therefore gone for all intents and purposes.
However, the workspace is a snapshot of a sessions contents, thus if you have code that made the sessions contents, presumably you could rerun the code and regenerate the data that was in the old session ?
Losing work, is always a painful lesson, those of us working with R/Rstudio long enough have had to learn to protect ourselves in various ways. I recommend using git to not only version control code, but to reliably restore it as needed. Also, I disable automatic workspace saving/loading. As I like to be in control of what is saved and loaded, and I treat project work that needs to be reproducible in such a way that I can generate the outputs assuming the inputs are available, and then I can reduce the requirements to back up large amounts of data, to just key input datasets that can not be replaced.
I'm sorry that this future looking advice is the best I can offer you with regard to the workspace session you have seemingly lost.