Well “us” might actually just be cooper all early s center around him..he also is the one that’s concerned with saving the whole human race..I also believe that last void was built so he could see the time he missed with Murph. And the big reason he took off at the end was bc he’s responsible for building or creating that void..when you think about it Only He would have so much confidence in his Own child to pick up all the signs knowledge

Well in the end Lucian found out the autopilot feature had been fixed some time ago Nolan always does that with endings he makes you unsure and leaves it up to the viewer.So Batman either killed himself or let Gotham Go with no attachments another thing is Lucian said it took a less occupied mind to fix it and Bruce Wayne had time when not being Batman