A few examples are Fable 3 (which can even become empty in the most literal sense), mass effect 2, or Fallout 3 (without dlc).
Sure, you can still do sidequests you haven't done before, but a thing that always distracts me is that a world which you just saved from its utter doom remains exactly the same as it was before, except for maybe a few new dialogue lines.
So normally, after playing through the game's mainquest, I tend to stop playing it even though there are still a lot of sidequests left.
What I would need to keep me going was new possibilites to open up. For example, after finishing the mainquest you can become duke of a city, get a castle which you could costumize, hire servants etc. Another way would be to open up tasks that keep you motivated, for example you get a map with certain items that you could combine to build a new sword, or you could get the task to kill off all remaining dragons/werewolves and stuff. Of course, the NPCs should react to you as their saviour properly and treat you with respect and esteem.
What do you think?