Hi Faelern. I'm really sorry. You spent hours building that family, then spent more of your evening trying to get it back. Starting again wouldn't give you those same characters or the time you lost, and I understand why an apology on its own isn't enough.
I reproduced what you described. You were right: clicking Load could overwrite another slot without you ever pressing Save or Overwrite. That was my game's fault. You didn't cause it by clicking the wrong thing, and you shouldn't have had to spend your evening figuring out what was happening.
I've now uploaded the fix. Loading no longer writes to your save slots, autosaves are stored separately, and I've fixed the missing event state that affected saves before ending a turn. I've tested switching between different saves and added backup history and file export/import.
I wish I could also tell you that your family is safely recoverable, but I can't promise that. The old version had no backup history or server copy. There may still be a copy among the remaining browser saves, but if those have all been overwritten, I can't reconstruct that exact family. The new backups can't undo a loss that already happened.
Please don't clear the game's browser data. If you're willing, use Load Game → Export Backup in the updated version to keep a copy of everything that's still there. I'd like to help check that data for your missing dynasty before telling you it's gone. You shouldn't have to spend another evening trying random loads to find out.