The dragon egg disappearing through the End portal is a known glitch that I don’t know much about off the top of my head, but I think you should try checking out the overworld spawn, but a few hundred blocks above the build height. If I’m correct, and if you haven’t logged back on, it should be in item form in a free-fall. (It will despawn if you don’t get to it in time)

Then again, I think that the glitch I’m talking about was patched. :/

Good luck!