If the ender dragon is gone, then there's an exit. Might have to wander around the main island a little the find it. Alternatively, if you have a chest or can get the wood to make one, put your stuff in it and off yourself.
Your a donator use cross world warp . Eg /warp world WebmasterMC -warp name-
That should bring you back . Hope this helped.
As mega said, but also if you're on vanilla (and if the end hasn't been reset) there will be a portal around roughly at you're 7-8 o'clock when you walk out of the spawn stairs bit. (I think).
You're safest bet is to do what mega said and cross world warp.
on a side note you can use it for warping across most worlds. The world names are on each of the portals in the spawn room (current map).
Nice little trick for jumping about warps and worlds quickly.
