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.