You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser.
ValveTime.co.uk | Valve News, Forums, Steam
Some quick shots I snapped from the 3rd Teaser vid showing what is left of C17!
In the video, the smoke is swirling around the flaming citadel, which makes me think that the portal was already opened when Gordon destroyed the transport, and the portal is now stuck open and creatures can come and go as they please!