Too hard to bring Alistair back. Either he's dead, exiled, or too busy as king or re-establishing the wardens.
Can't bring Morrigan back - well you could if you turn down her ritual offer (and thus either you or Al died), but even then, I still think they won't.
You know Wynne's on borrowed time. Not only is she elderly but heck is just some Fade spirit keeping her walking & talking, she's practically already dead.
Yes I'm rooting for the return of Leliana, especially for people who romanced her & are continuing their savegame, but ... doesn't seem in the cards.
Return of Zevran .. esp. for female ... or male ... players who romanced him, dunno, but likewise. If he's getting written out of the story, it's because I predict the Crows caught up with him and "dealt" with him, after all.
Sten... well, he kept saying he was going back to the Qunari homeland after the Blight, you have to figure he did.
Loghain ... really couldn't care one way or another ... killed him on every playthrough, NEVER took him as a companion, I don't forgive easily.
Rooting for the return of Shale & Dog, but if you bring back Dog, I would expand his talent range so that at least like Shale he has 16 talents instead of just 8. Maybe if you're a new Orlesian warden there's a way you come across a new, loyal & faithful Mabari all over again. Although other "Pet" options might be cool too... like a Pet Wolf.
It seems it will be Oghren coming back ... ehhh, loved his dialogue, his bluster, why not, he's not the one I would have chosen first to come back, esp. if it's only him, but oh well.