No portal from dragon area to then rest of the end

On my realm (talkingmuffin47's realm) we went through  the end portal and began to battle the dragon.  The dragon spontaneously died after about three minutes and opened up the portal back to the overworld.  We have searched the dragon area over and over and are unable to locate the portal that takes you to the rest of the end (ships fortresses etc.)  Thank you for your time and I hope that there is something you can do to fix it.