The fallout style, where the game actually ends (good or bad doesn't matter), allows much better storytelling and quest design. In FONV so many quests ties into the main quest, weather you do them or not, and weather they have an *actual* impact on the main quest outcome or not, making them unplayable after the dam. I.e. the Boomers, where you
Spoiler get the plane, artillery piece, and their support
in preparation for dam and who you side with, wouldn't make sense to do after the dam. Or Return To Sender (Chief Hanlon), although the outcome didn't matter, it still felt connected.
In FONV, even if you avoided the last boss fight and simply talked him out of it, the story and fate of those you've met are told, in a really grand way. It was an ending to remember. In TES, although you may remember the end of the main questline, you don't remember how the *game* ended. For me, they always just kinda faded away. Not memorable at all. Kinda sad.
So for me, the grandest ending of all times in an RPG, was FONV followed by FO3 (just *bald* to let the hero die
)
I guess what could have worked out in Skyrim would be:
* Double Main Quest - Alduin and Civil War.
* FONV endstory for each Main Quests.
* Continue to play after both Main Quests, but with consequences.
* Replacement cells where needed when either of or both are completed.
In FONV it would translate to: Continued play after finish. New Vegas and main camps cells replaced with new cells depending on the outcome. Most quests connected to the main quest would be set to inaccessible, and most important people replaced. But it still would be pretty little stuff left to do unless they made side quests specifically for the after story.