There is a 'ditch' button that when pressed automatically closes all the various openings in the aircraft, rendering it sealed. In this case, the front exit only was used to prevent swamping from the rear. The plane remained floating at least 5 minutes before some settling began.
As for discussing survivability, lets look at the 'injuries' which were hypothermia.I am saving for a specially made survival suit for air travel. You can view it @ www.bookster1uk.com