Try working internally with your IT department; sometimes they can grant temporary access to the registered email to log in as the administrator that left your company. If this is possible, you can reset your account password from https://supplier.coupahost.com/forgot_password and log in as usual. However, if you can't obtain access to the old email, ask your customer to update the primary email address on their side for you as a supplier, proceed to "unlink" from the old account, and then "relink".

All the transaction data remains. Some basic company information and payment locations/details may need to be updated in the new account, but most of the important information and transaction details are carried over automatically to the new account. For more information, see Create Your Account.