How do existing JomSocial users connect their FB accounts?

I understand that you don't want users to be able to login. To get the permissions for a Channel though, that's the only time we do it. I can't imagine it would be a problem in normal circumstances though as you just need to enable Facebook login temporarily to get one user's permissions to post on their behalf. After that, tell that user not to remove the application. I don't know you're full setup, but I'm assuming you have immediate access to the user who owns the Page, so it's one restriction for that person. Or, have them add you as an admin on the Page so you can grant permission.

So in our case, if a user connects their Facebook account, then goes to Facebook and revokes the permissions, there is no way they can later reconnect to that specific Facebook account?

No, that's not accurate. The Re-Connect button will let them re-associate the Facebook account with their existing Joomla account. The special additional permission to be able to post on that user's behalf to a Facebook Page they own is only done during a normal login, not a connection process where the user is already logged into Joomla. The additional permission is only requested from user's that have a Channel setup for them which, from above, I'd assume is not many people.

Thanks,
Alex

Sorry, I think I went off on a tangent a bit when you said "Well, except now when I connect it and make a post, the post does not go to Facebook."

I was thinking you were using the "Channels" feature, which requires an additional permission from Facebook to function. Let's step back and help let me know what you mean by "connect it and make a post".

As to the flow of a user removing your application from their Facebook profile, they should be able to:
1) Login to your site with Joomla credentials
2) Use the "Facebook" button from the SCLogin module to re-connect their Joomla account to their Facebook account
That last step is what our code fix above helped to fix and should be all you need to let a user (re-)connect their existing Joomla account to Facebook without the need for showing the Facebook login feature always. Now, with that done, what posting are you talking about. We support a lot of different ways for posts to go back to Facebook.

Thanks,
Alex

I believe you shouldn't have a problem with that. You mentioned above that you did, but not sure why that would be. Please keep testing and if you do, let us know, we'll gladly help investigate further.

Thanks,
Alex