You should definately be able to continue after the main quest, and I'm sure we will be able to. I suppose you probably brought up the subject because in Fallout 3 before Broken Steel and in New Vegas, the game ended with the completion of the main quest, but what one must remember here is that those games are Fallout sequels, not Elder Scrolls sequels, and both series have some differences. There have been arguments that Obsidian's decision to make New Vegas end with the completion of the main quest, but these arguments are made with the Fallout series in mind, and don't really work in the Elder Scrolls. For the Elder Scrolls, not being able to continue playing after the main quest simply would not feel right. It's not simply because you wouldn't be able to do side quests after completing the main quest then as you could simply finish all side quests before completing the main quest. The main problem with not being able to continue playing after the end, for me, lies in a fundamental aspect of the series, which is that there's a lot more to any Elder Scrolls game than the main quest. Usually, the main quest is the major storyline in the game that's going to help shape the future of Tamriel, but without the side quests and guild quests, the game would just be a bare core, the game is not just the story of the main quest, it's the story of your character, from the beginning of your adventure, to whatever point you decide to end the story, it doesn't have to end with the main quest, though if you don't want to continue playing the game after the main quest is over, that's your choice to make, and that story is shaped by your decisions, having the game end after the main quest would be a break from this trend, as it implies that Bethesda has chosen to put the focus on the main quest, with everything else just being extra, even if there was the same amount of content from side quests and such, it would still feel that way, because as a rule, stories end when the point of the story is over, and there's nothing more to tell, usually, you'll get an epilogue to show the aftermath of the story and what the characters are doing now that the big evil guy has been defeated and the world is safe, but it's not going to just keep going on and on with nothing especially interesting happening, because that would be boring. At the same time, if the story just stopped in the middle of the action without actually resolving the plot, it would seem a pretty unsatisfying conclusion. So generally, stories end when everything has been wrapped up, and if you look at a game as an interactive story, and the game ends once you've finished the main storyline, than that implies that the main storyline is the storyline of the game, and everything else is just extra, and this is fine, for most games, but for the Elder Scrolls, it's not. If an Elder Scrolls game ended with the completion of the main quest, it would seem to signify that the series has changed its focus from an open world sandbox with many side quests and faction quests and a main quest, if you choose to pursue it, to a central story with some side quests you might choose to complete if you like. And what follows then? Cut out the open world exploration entirely and turn the game into a linear RPG?
Frankly I'm worried about the legions of people willing to sacrifice authorial integrity and an actual climactic ending just so that they can go mining after finishing the MQ.
I'm more worried about the people who seem to think needlessly killing characters is the only way to have authorial integrity and a climatic ending, myself. And I'm worried about the people who seem to be entirely missing the point of the Elder Scrolls, perhaps you'd be better served by playing Dragon Age or something.