They will not get unenrolled for eStatements, but their email will be marked as a wrong email address. This will cause the member to receive a printed statement that month, and the normal e-Statement fee/rebate will not be posted.
The next time they log in to online banking, they will see a banner ad alerting them to the fact that their email is flagged as "invalid or missing" and that features such as eStatements require a valid email.