You are wellcome my friend. -And thanks for the additional information. -I share the same wish.

I can't speak for Android version but in iOS version steps for offline play is as follows:
1. Login once to the server while online.
2. Quit game
3. Turn off all internet for the device (wi-fi and...

The mobile version already has an "play offline option" but it requires to login online first (and I don't know if it will require in the future). Where as for PC, I couldn't find an offline option....

A Final Wish from Shadow Era Fans

Dear Developers, Producers and Managers of Shadow Era,

Please, make Shadow Era payable offline on mobile and PC after the official serves shut down.
...