The questions went something like this:
1. Is there another "unknown planet" named "Nibiru" that may collide with Earth? (see below for answers!)
2. Are there any currently known solar system objects that could collide with Earth?
3. How will Earth eventually be destroyed?
#1. No. Astronomers have gotten very good at detecting dwarf planets beyond the orbit of Pluto & they are discovering new dwarf planets (as technology improves) frequently. No huge "Nibiru" or "Planet X" has been found nor likely will be found orbiting our Sun.
#2. Maybe. The double-stadium-sized asteroid named "Apophis" will get very close to Earth in 2029 & again in 2036. The 2036 date has a very small but real possibility of colliding with Earth (won't know until after 2029). Even so - a collision of that magnitude - although large in consequence - would not cause the "End of the World (as we know it)." However - NASA has been operating a program to detect other NEO's (Near Earth Objects) for years & have a pretty good grasp on asteroids/comets that may be coming our way (see website for a possible 2040 collision!)
#3. Several possibilities for Earth's destruction. That means a complete destruction as in - no more planet Earth. Most likely the Sun will start to run out of hydrogen fuel in it's core & expand. This will swallow up Mercury, Venus & probably Earth - but there may be tidal interactions that will allow Earth to escape. Into what? Maybe into a collision with Mars. When will this happen? About 5 billion years from now. No need to pack your bags just yet.