Your saved .stg and .dds files for your map won't get you diddly at this point.
IF you DIDN'T DELETE your level_level name_autobackup folder in AppData\Roaming\SpinTiresEditor, you can recreate the xml...PARTIALLY as it was just with that. It's a relatively simple process in itself(that much of it at least). But what you won't be able to recover with it is anything on the map that was set in a particular place on the map(stay with me, it's not as bad as it sounds). You can only recover the things that are autobackedup with a dds(height, tint, water, water mud, mtrl base/new, and dstr). Locators, models, plants, overlays, rivers, references, trucks, and routes would all need replaced by hand(since what they are, and where they are on the map, is stored in the xml).
Create New Terrain. Make it the same name and size as the map you want to recover the xml for. Allow it to create a new .stg. Open the folder for it in prebuild and delete all the files in it. Place the latest backups(highest numbered, NOT labeled src). for height, tint, water, water mud, mtrl base/new, and dstr. Rename them so they look exactly like the ones you just deleted(no _number or _src at the end of the names). The _src files are blanks. If you left the whatever blank the latest backup would be the _src(if not it's the one with the highest number). Basically just ignore the _srcs. They won't get you anything. When you've got all the files in the prebuild folder replaced with the latest backups, add all the backed up stuff back(for every dds file add the whatever it was to the terrain). JUST ADD THEM. Don't bother rebrushing them. Then rebuild terrain. Now you will have your map back, but without the stuff found in the deleted xml. Then save it. Now you'll have an xml for it too. Then you need to go in and replace all the things on the map that have placement coordinates stored in the xml(mentioned above).
I may have forgotten something or not figured out what won't work with the process. But I'm pretty sure it will work exactly as I'm saying. Worth a try at least.