My world was once analogous to our own Earth, where life evolved in the light and heat of a nearby star. Unfortunately, a cataclysmic event knocked the planet out of orbit and sent it spiraling as a rogue planet into the dark, limitless void of space. Luckily, some of the inhabitants survived this cataclysm.
I need your expertise and scientific knowledge to help me answer a few questions about the feasibility of this.
What cataclysmic event could dislodge a planet from orbit around its star without instantly exterminating all intelligent life? What conditions could improve humanity's chances of survival in this scenario? (E.g. living in bunkers deep within mountains?)