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:

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…

Thank you for your patience.