PhD (Dr.) student willing to finish thesis after several years of inactivity
Did you ever experience a PhD handing in the thesis many (>5) years
  after completition? If yes, was it accepted?


Our department actually just went through this. Our process involved a justification of why the gap occurred, a defense of the student's standing both at the time the gap occurred and now, and a defense of the scientific merits of the research (and how it wasn't completely stale).


  If it was accepted, has it been evaluated based on the state of the
  art when the thesis work was done, or based on the current state of
  the art?


Current.