Glad to hear the importing issue is fixed. I hate providing code changes, as it's best to just get a new release out, but that takes time to test and get ready.
As to your question about Facebook logins from JomSocial, unfortunately, JFBConnect can't just go through and re-issue everyone a Joomla password for their account. It may be a possibility, but like you said, poses some issues with email everyone those passwords and general logistics of generating them all.
For users created from JomSocial, Joomla will not even show them a 'password' field if they go to edit their profile. However, if you're ok with running a SQL query on your site, you can trick Joomla into showing the "Password" and "Password Confirmation" fields on profile pages for users that don't have one. The query is:
UPDATE <YOUR_PREFIX>_users SET password = "xxx" WHERE password = "";
That sets the *hashed* password value to 'xxx', which would not work out to any real password for a user. What you're essentially doing is setting the password field to garbage, but as long as it's not blank (what the WHERE clause is looking for), then Joomla will think the user already has a password and allow them to update it.
Once that's done, you simply promote the fact that the user can select a password and login. There are probably ways through a template override of the User Profile page that this is also possible, but I don't know how off-hand.
I hope that makes sense, but if not, let me know,
Alex