Mathew Santoro's Forehead

At the moment, some friends and I are playing together on a privately hosted co-op server. However, we can only play upon invitation from the admin, and only when he is in the server, if he leaves we all disconnect. Is there a way to have the server up and running 24/7 or even just without the host having the game open. Any replies appreciated, feel free to add me on steam if you're able to help (http://steamcommunity.com/id/chikonwingxx/)