Hello @phenris ! Thank you for taking the time to send us your feedback on the game. Private lobby is highly requested: our team is now aware of it and figuring out what to do next.
I hope you still enjoyed the game itself and that fighting off the zombies was fun!
I'm very sorry to say we can't recover your save files for you. We would recommend that you back your saves up until we get a 100% fix on this.
Your saves are located here: \AppData\Local\Saber\WWZ\client\storage
Appdata is a hidden folder located in your User folder.