Bonnie was done with originals trying to play with her and her friends life, so she sends Klaus to the future when she and her friends have lived and died, well, that's what she thinks at least.

I never liked Elena killing Kol but I can't blame her for that either, she was desperate, her brother's life was on the line, either Klaus was going to take her brother for a never ending Vampire hunt which would have ruined his life or Kol would have got him killed. What if Elena was not so desperate, what if Elena knew about the prison worlds. Read and enjoy. Kolena and Klena.