I was wrapping up my exploration of the caves west of Barovia, and when I went to reload the file, the game suddenly tells me it can't restore the map. No more named save file, either. I had been saving and loading pretty frequently in the same session without issue, so I'm a bit confused about what happened. Checking the save folder reveals that there's several level data files (probably the maps and what I've explored of them)., but no "SAVE.DAT" file like there is in the other folders.

I do have a backup save which I updated earlier today, but even that seems to have reverted the data to the first night I started playing, not where I had saved it earlier today.

Is there anything I can do to restore my progress, or am I screwed?

Well, I essentially restarted, this time making certain to backup my save file in a separate folder altogether after each play session, or every couple hours. Unfortunately, the issue very nearly happened again just now, except this time I noticed the empty save slot as I was about to save my progress, not reload it. Other times, I've had the same error message as before, but the filename is still there, and so retrying will still work. Either way, It's quite aggravating that I have to take these extra precautions. Fortunately, I seem to be near the end of this game, but it's left a bad taste in my mouth.

Anyway, what I did was I load up my earlier save, went through the caves west of Barovia again, then copied the map data from before. Doing this, I noted that the copied maps retained all the previous info, such as the enemies killed and the items obtained, yet the inventory items and EXP from the enemies didn't transfer over - I'm guessing that stuff's in the SAVE.DAT file (that meant the keys and other important items were gone). Anyway, I didn't care to re-explore Barovia again, which was my main reason for copying the map data, although I did make sure to do all the important events in town that I did before, else I may have been screwed down the line (when I first copied the map data, I was able to re-initiate the first event at Castle Ravenloft, minus the scene where you get the Iblis Key thingy from Strahd, which meant I couldn't leave - Doom Guards were still stationary).

Into which directory did you install the game?

Well, I managed to finish the game a couple days ago, but to answer your question:

E:\Ravenloft - Strahd's Possession

Subfolders are DOSBOX and RLOFT, with the latter containing the subfolders for the save files.