>> - Is it a good idea to make sure that when players do exit (which is inevitable), it's a satisfying exit?
no harm in it.
>> - How can we determine when a player is ready to exit, so we can present the exit, before she continues playing beyond her point of enjoyment? (ideally, we want to encourage use of the exit before the game gets boring, but after he's had as much enjoyment as can be mined out of it)
nigh on impossible. its hard to say when they will get bored. you might assume they won't get bored until they run out of content, but that's not even a safe bet. they may not be into the content that remains, or they may not have even found it.
- How can we present the exit in a way that players comprehend well?
shouldn't be that hard. reminds me of Sol (Edward G Robinson in his last film) "going home" in the movie Soylent Green with Charelton Heston.
just be sure to make it obvious. i accidentally ended fallout 3 twice by completing the rather short main quest line. and the second time it was unintentional. i found myself at the final quest without ever actively pursuing it.
- Is this actually beneficial for the developer?
for the developer, no. its more work. and its not enough of selling point to significantly impact sales.
it seems you like closure. there's no harm in adding optional "closure" features to a game. but then again, in real life - the ultimate rpg - there's no closure, no exit for the bored (if there was i would have left this god forsaken rock long ago - i'm just doing time on planet earth). the only exit is suicide. so you keep playing til you drop or you're so bored / disgusted / without hope you cap yourself.