As I was digging tunnels around the End Island, getting ready to fight the dragon, I noticed that the End Dragon Health Bar would sometimes disappear for a bit. I figured it might just be a case of the dragon losing my presence and "stopping" the fight, so I didn't worry about it. I had blown up two of the end crystals and was getting ready to start digging up the third pillar when I noticed that the dragon health bar has been absent for quite a while. I came back to the surface, and the dragon was gone. No egg, no experience, and no portal to the outer island, but the main portal was active. I hopped in the portal, skipped the cutscene, and as soon as I arrived back in the overworld, there was the dragon! And I was dead. Repeatedly. After unseccusfully trying to salvage enough of my base to find a weapon to kill the dragon with, I ended up just chilling back and watching the world slowly collapse under the attack of the Ender Dragon. 

I wasnt able to get any really good pics of the dragon, but here's my in the overworked with the dragon's health bar, checking out some of the holes he'd dug already.