You can not play Diablo Immortal offline. Players need active internet connection(Mobile data, WiFi) to play Diablo Immortal. Game shows server connection and network connection error in offline game play.
Diablo Immortal server connection error
What happens if I open a Diablo Immortal game without internet connection(Mobile data, WiFi)?
Here, the game will display a server connection error message with an OK button to close it. Following is an error message.
Unable to connect to game server. Please check your network or select a different network.
Diablo Immortal connection failed error
Next, if you lose your network connection while playing Diablo Immortal, then the game will display the following connection error message with Cancel and Retry button option.
Connection failed. Please check your network and try again.
Retry option to re-connect and resume game:
Here, Retry option to connect network and resume game available for 10 seconds. You can click the Retry button within 10 seconds to connect and continue the game.
After retry, if your device is not connected to the network, then the same error displays again and you can retry again within another 10 seconds.
What happens when I get the network back in Diablo Immortal?
When you lose network connection and reconnect back in Diablo Immortal, then you will be returned to the same place in game.
Note: In this disconnect and reconnect time, time still moves within the server. It means, enemies can still damage you.