Of course I clicked that "Delete Campaign" button (and the popup "Yes, I am sure" too), while I just wanted to save scum a couple of game hours earlier and delete a few "dead end" saves, after being obliterated by a scourge rush. Aaaand I exited the game instead of killing it from the task manager, which let steam cloud sync overwrite my cloud saves, killing any hope of detecting a conflict between cloud/local saves on the next run.
Entirely my fault, though I think 2 "delete" buttons on the same UI component can be a recipe for frustration.
I recovered some saves (including autosaves) with Recuva, recreated a campaign folder but they look corrupted (serialization errors / index out of bounds). At least I scavenged the galaxy layout seed from an uncorrupted '.savemet' file !
