I feel as if these answers have been less than helpful.
How many IN GAME YEARS- will the story cover. Me thinks it should be a while.
It can't be too long. With the Breach it is virtually a ticking time bomb over the heads of Ferelden and while I imagine Ferelden will suffer another scar from the breach, it can't be, presumably, too much of a one because BioWare will want to leave that door open for Ferelden to appear in future games or future DA media. I mean yes, there should be some endings where the world goes to hell but most of those endings probably won't be chosen in canon and you will not be able to import them into a future game...so long and short answer, depends on how quickly the Breach is growing.