Can the entrance elevator be removed?

In Fallout Shelter, is it possible to remove the elevator at the entrance to the shelter and replace it with a room, or is it there to enforce depth growth?

Can it be done if I send everyone out to the wastelands and remove all the rooms?

Simply sending them into the wasteland won't be enough. This is because even though no one's there, the game still requires you to maintain enough living spaces for your population. So, you can't destroy the barracks which attach to the elevator, preventing you from destroying the elevator. If you were to kill off (and delete) all your current dwellers this may be possible.

In a new save game I was unable to kill my starting dwellers with fire. They seem totally impervious. I've sent them out into the wasteland for now, where I can only assume they will not last.

Edit: Well, there were no survivors. With no dwellers remaining, I was able to delete the elevator and replace it with a different room. You may make a great looking vault, but you're unlikely to win any Overseer of the Year awards, having killed off all the existing dwellers. The vault can be repopulated, so it's not a game over scenario.