this is the original email of devs on steam:
Officers! IMPORTANT ANNOUNCEMENT!
Blitzkrieg 3 is going offline! We present you the new offline Blitzkrieg 3 build, which will let you enjoy tactical battles of this WWII strategy without having to be connected to the internet. The offline version has all the features, content, and your saved progress from the online version – except, of course, the PvP online mode. However, should you choose to compete, Boris will still be happy to assist you in a friendly duel, opposing his AI skills against yours.
After you download the latest update, you will have two options at the start of the game – to play the original Blitzkrieg 3 or to play the offline version. Please be aware, that in order to transfer your current progress to the offline version, you have to upload the patch and to run this mode, while the online Blitzkrieg 3 is still available. The servers for Blitzkrieg 3 are planned to be shut down in the recent future, so please don’t put it off. The exact date of shutting the online Blitzkrieg 3 will be announced additionally.
We hope that you enjoy playing Blitzkrieg 3 offline and wish you splendid victories!