Even though the email account has been deactivated, you will still be able to login to your social networking account. This is because as long as the email and password match, you can login to those sites.
The bad thing is that if any of those social networking sites send email to the deactivated account, you won't be able to see them. And, if someone has registered for your deactivated account, they will be able to see those emails!
I would recommend you try and reactivate that email if you can. I would also go into the settings on the social sites and turn off any unnecessary emails they may send to your deactivated email address.