I would prefer none of them returned. Varric is cool, but anyone who may have formed a deep, even loving, connection to a protagonist from a previous game shouldn't come back with the Warden/Hawke mysteriously absent in their lives.
It makes the previous games feel meaningless and sidelined. This is why I feel it's lame to bring back Leliana and Morrigan. These two just happen to be intimately involved with another Thedas-shaking event? Please.
Leliana shouldn't be back at all if she's already dead.
I think it would be bizarre for Morrigan not to play a significant role in Inquisition. Mike Laidlaw said in the Game Informer interview that there are too many loose threads that need to be addressed before the writers can introduce new mysteries, and I agree. Even though Morrigan was one of the central protagonists in Origins, we know next to nothing about her.
Is Flemeth really her mother? Who is her father?
What is Morrigan's agenda? Is she working in concert with Flemeth or against her?
What did Morrigan hope to achieve by performing the Dark Ritual?
Where did she travel to at the end of Witch Hunt? Where does the Eluvian lead?
What secrets did she discover in Flemeth's Grimmoire?
For those of us who performed the Dark Ritual, what is the fate of the old god baby?
And yes, it does make sense for Morrigan to be involved in this "Thedas-shaking event." As Arcane adviser to Empress Celene, she is more highly placed than even Vivienne.
Lastly, Mike Laidlaw has said that BioWare knew the core of the Inquisition storyline, which he described as the Morrigan's "moment," since "midway through Dragon Age: Origins."