As to fixing your current problem, this is why one should save their files with incremental file names - character.1, character.2, character.3, etc… This way, when making drastic changes, you can always back up to a previous copy. Additionally, if you have a file named ‘file.blend’ and you make changes to it and re-save it, blender will take the previous file, and rename it to ‘file.blend1’. Blender does this automatically and always renames the last 2 files as ‘file.blend1’ and ‘file.blend2’. So if you choose to open a file in blender, select the directory containing the file, then at the top of the file browser, there are a series of icons, look for the one that look like a funnel, that is the filtering icon. Clicking on it and you will now be able to see these .blend1 files and can open them, allowing you to back track.
Now, as to your original problem, the bone weighting fail, rather than look for other ways to do this, why not look at why it failed. Auto bone weighting will fail if there are double vertices or if you have parts of the mesh that overlap other parts of the mesh. Like a hose for example, you’d have faces making up the inside of the hose, and faces making up the outside of the hose. Blender would never be able to auto weight something like this. For something like this, or you problem, you could just manually weight it using weight painting.