sorry, not pessimistic, its just that the magnitude of everything needed to dismantle the planet is so huuuge that there is no way that we could sustain our civilization during that period. Currently we can barely change trajectory of an asteroid.

Speaking of them, even with already available raw materials from asteroids we couldn't use it because it is spread all over our solar system. collecting all asteroids would be like moping the room and collecting 2g of dirt.

We are still ages from planet killers and dismantling planet will take even more time to be viable.

Currently we are creating tiny lines in Earth with our mines burrowing the crust.

To dismantle a planet we would need resources and tech that is out of our grasp, our civilization will perish long before that is achieved.