All the scientists on the radio seem to talk about ‘when the sun grows into a red giant then…’, but what exactly

Question: All the scientists on the radio seem to talk about 'when the sun grows into a red giant then...', but what exactly would happen if the sun left the solar system?
- Keywords:
  end of the world,
  sun
Asked by [▀̿Ĺ̯▀̿ ̿]#JoinTomBoy[▀̿Ĺ̯▀̿ ̿] TGS to Connor, Jillian, Lidunka, Sarah, Steven on 18 Jun 2015.
- Lidunka Vocadlo answered on 18 Jun 2015:
  
  If the sun left the solar system (how this wold happen I have no idea) then we would have no sunlight and the earth would freeze to about -200 degrees within a few days. We would also fly off at a tangent because we wouldn’t be orbiting anything any more.
- Jillian Scudder answered on 18 Jun 2015:
  
  It’d be hard for the sun to leave the solar system, but assuming that it did manage to vanish and leave the planets behind, our planets would quickly drop in temperature! We would stop orbiting around a common point (unless the sun were replaced with something equally massive) and fling ourselves out into the galaxy to wander forever as cold hunks of rock.
- Steven Thomson answered on 23 Jun 2015:
  
  The Sun is the centre of the Solar System, so it the Sun moved it would take us all with it!
  
  In fact, the Sun actually is moving – it’s moving really quickly, orbiting the centre of our galaxy, and our entire Solar System moves along with it.

Question: All the scientists on the radio seem to talk about 'when the sun grows into a red giant then...', but what exactly would happen if the sun left the solar system?