Apple has added some additional information to the Developer Portal’s maintenance page stating that memberships that were supposed to expire during the unexpectedly-long downtime have been extended to accommodate for the issue and apps will remain on the store until the portal is available again and developers can properly renew their accounts:
We apologize that maintenance is taking longer than expected.
If your program membership was set to expire during this period, it has been extended and your app will remain on the App Store. If you have any other concerns about your account, please contact us.
Thank you for your patience.
Update: Developers with memberships set to expire while the portal is down have received emails stating they have received a one week extension. This may indicate that the downtime could drag on for a few more days…