Hi,this is the solution if your launcher doesnt want to ask for offline mod:
1. Turn off your internet connection/router/modem(i dont know what it is called xD )
2. Open the Launcher
3. Enter your Nickname in the Username field
4. Click on Login
5. Then it will ask you for the Offline or Online mode,click offline
6. Wait for the Main Menu screen
7. Connect to internet again
8. Enjoy :)