Save files are stored locally on your system still. The files may have become corrupted in some way causing it to not load properly.
All global data such as stash and crafting materials are stored in a single file.
Each character has their own file.
I don’t have the exact path on hand but it should be on our support site if you look for file locations.
If you’re using Steam cloud saves, it’s possible that they have a backup or that it was that which caused the problem in the first place.
The game does keep a backup save in the same location that could have the data in it too.
Because the saves are not stored on our servers, it’s very unlikely that we can do much to help get it back but I hope this info gives you a leg up.