(I don't think you can get another dragon egg or the insane amounts of XP for killing the dragon if you have already killed it once, though I'm not certain about that.)
For this you have to edit level.dat to reset the status of the dragon, which makes it sound like it may not respawn or the fight may not work properly if you just delete chunks (at least in 1.6.4 the dragon is spawned when the chunk at 0,0 is populated), as well as data pertaining to End gateways, which may also not regenerate if the game thinks it already created them (presumably, you can just delete the entire "DimensionData" tag, or its "1" subtag in the case they ever add more dimensions with special data. Obviously, always test on a backup):
DimensionData: This tag contains level data specific to certain dimensions.
-1: Data for The End
--DragonFight: Data for the ender dragon fight. Only appears after the end is entered.
--ExitPortalLocation: Location of the End's exit portal that the ender dragon flies to upon it's death
---X: The X coordinate of the portal.
---Y: The Y coordinate of the portal.
---Z: The Z coordinate of the portal.
--Gateways: Contains a list of locations of the End gateway portals that haven't been spawned.
---: The angle of a future gateway, from 0 to 19. 0 is east of the exit portal, and numbers increase clockwise.
--DragonKilled: 1 or 0 (true/false) - If the dragon is currently alive.
--DragonUUIDLeast: The least significant bits of the current Ender Dragon's Universally Unique IDentifier. This is joined with DragonUUIDMost to form the dragon's unique ID.
--DragonUUIDMost: The most significant bits of the current Ender Dragon's Universally Unique IDentifier. This is joined with DragonUUIDLeast to form the dragon's unique ID.
--PreviouslyKilled: 1 or 0 (true/false) - If the ender dragon has ever been defeated. Used to determine EXP given by dragon
I'm not sure about more recent Minecraft versions, but years ago (maybe with version 1.6 or 1.7 or so?), deleting that folder was seemingly a full reset on the End dimension, including the dragon (at least to some extent). I would delete that folder, and having been defeated, it would come back. It was possible to get more eggs and experience (the latter being what I was after) this way. I don't do this anymore, though, and it sounds like things have changed.