In order for the Earth to be thrown out of it’s orbit, it would requite something massive to swing by it. Something like another planet or a large comet. The last time this happened, we think this wiped out the dinosaurs but didn’t change the Earth’s orbit.
If this does happen, we would become on a direct collision course with the sun or another planet. Like playing snooker with planets! We’d all frazzle due to the heat or the impact with another planet would wipe us out.
That won’t happen though. NASA’s eyes are trained to the skies and are watching closely for any big object to pass close to us. If it ever does, we’ll try and defect it somehow. I’m sure the boffins at NASA know what we should do 🙂
I think it would affect the temperature on earth quite substantially. The distance from the earth to the sun does not vary very much through its orbit, but because the earth’s axis of rotation (causing day and night) is at an angle, this causes the seasons. So there could be BIG changes in climate if the earth’s orbit and its angle of rotation changed.