I was once 3 hrs into a 9hr flight when we turned back to base. Captain explained that the tech problem would not stop him from continuing but that the a/c would then become AOG away from base which in itself would cause ops all sorts of logistical problems. We were promised that a spare a/c and crew would be waiting for us. And so it transpired. After 75 mins on the ground we were on our way again. Well organised and at least the pax on the return flight were not inconvenienced any more than we were.