What is destroyed when resummoning/respawning the Ender Dragon?

I'm coming back to Minecraft after a long absence, and pursuing new objectives and opportunities. I've read that one can respawn the Ender Dragon, and I'd like to do this at some point. In order to prepare as best I can for the fight, and not lose resources unnecessarily, I'd like to know what parts of the End will change when I resummon the Ender Dragon.

1. Will the exit portal stop working?

2. I have read that the tops of the obsidian pillars will be reset to their original form, destroying any added blocks. What are the dimensions of the volume that is reset?

3. Is there anything else that gets modified besides the exit portal and the tops of the pillars?

1. Yes, in that the portal disappears, but no; You can still teleport to the End Islands using the End Gateways (the ones you use Ender Pearls to teleport out into the islands), and exit the end itself by spawning in a portal (/setblock ~ ~ ~ minecraft:end_portal)
2. For the 11x11x14 (WxLxH) area from top of the pillar (this is from where the top of the iron bar cage, even if it spawns or not), it removes ALL blocks. Anything below that, only the obsidian pillar itself is replaced. All surrounding blocks remains unaffected.
3. The End Gateways lose their beacon effect, but still work. Also, they don't disappear.

dying

Still a way to get out. But once you hop back into the End again, you can't leave until the dragon is defeated. That, and you lose your items (from death, obviously and if you don't have /gamerule keepInventory true on).