More details can be found at Word to the Wise (a great deliverability resource, btw)

The bad Roadrunner email addresses were automatically removed by MailChimp when they bounced back, so there’s nothing you have to do. Note that you can’t just take an old @roadrunner.com address and switch it to @comcast.com.

Let Your Customers Submit Change of Email Address
This might be a good time to look into adding an “Update your profile” link to the bottom of all your MailChimp newsletters. That way, when your customers change their email addresses, they can log in and update their information on your list if they want to continue receiving your campaigns.