The project file is really a text file and it can often be repair ...or it has been repaired in earlier versions....by copying and pasting sections into a new project file. But that takes some understanding and study of the layout of the project file which can be understood by looking at a simple one and comparing it to the one needing repair. It might mean losing a model,material ,action,ewtc that is corrupt but most of the project could usually be saved. I remember doing this for a few projects in earler versions.