Loans and mortgages are commonly sold to other companies. When this happens, simply add the new company that now owns your loan or mortgage to your Mint account so you can view the information once again.
Don't forget to mark the old account as closed! This will let you keep your historical data but we won't get information for it any more.
Click here for more info on how to add an account.
Click here for more info on marking your account as closed.