Ligend,
Right now, the SCLogin module will display only the avatar you set for it to display. If that doesn't work, then no avatar will be displayed. There is no 'fallback'. If you have JomSocial, we'd recommend setting the module to display the JomSocial avatar. That avatar should be populated either by the user manually or by JFBConnect by importing it for them. If you set it to use just the Facebook Avatar, then it will show no picture for those that haven't connected their account.
I just looked at the code for the SCLogin module. and it should show the JomSocial user's avatar whether they've logged in using Facebook or not. If that's not happening, let us know.
As for the avatar not displaying in K2, I have no idea about that. I'm not sure that issue is related to JFBConnect.
Hope that helps,
Alex