I have kept all my characters alive or with the group in DA Origins, and the only character that ended up leaving the group in my DA 2 playthrough was Fenris.
With both games there where characters, I really enjoyed, that annoyed me, or where part of the group and I never used them. With nine different companions, two or three members for each class (Warrior, Rogue, and Mage) and 40 possible endings, I think I can afford to keep the companions I want and ditch the others. My first playthrough for both games wasen't "exactly" how I wanted it to end but, I love how it came out. I plan to make my first playthrough of DA I interesting enough for me to enjoy the outcome. This time, I don't see myself having a full party at the end.
However, I think i'd have to consider the ideals and goals for each character and how, it would suit the ending of the story Im trying to build. If, I keep a character around because, it prevents a riot, secures an area, or gains more allies to the cause are questions I would consider for each party member. This time around I don't see myself tolerating an apathetic mage, an elf taking his hatred out on an entire class, or blood magic users unless, it serves my purposes. It's cool to keep everyone but, I don't see myself doing this time around.