What happens to logins if you use expired e-mail (for a forum or website for example)? I suppose a user would not be able to receive e-mail. But does a website even "care" that the e-mail address is expired? Will logins still work for the user?
Once the site account is setup and validated you could technically delete that email account. To the site a user's email address is just a piece of data. It would affect a number of features of the site though including the ability to reset your password and also to receive notifications.
You're probably screwed if the company that provides the email you used on the form is no longer around. Maybe that forum has other means to verify your account? Maybe you can contact the forum admins and they could help you out directly?