No one died my first time. If you import a Shepard and just...do everything, then no one should die. Well, and you have to make the right choices on who leads the team. The Squad leaders and tech/biotic specialists are obvious. However, the game doesn't let you know to leave behind your strongest defenders (Garrus, Grunt, Zaeed. Don't take more than one) for the final part of the Suicide Mission. Taking more than one defender and leaving too many weak defenders (Tali, Jack, Mordin) makes it possible for one of the people in the latter group to die.
Anyway, on my two main characters no one died. But I've experimented in other times and had some die. Tali died last time while escorting people back to the Normandy. I failed to gain her loyalty because I wanted to try exposing her father. She didn't like that.
I also let everyone die once just so I could see it. No ship upgrades, no loyalty, wrong squad choices. It was a slaughter, and Shepard died too.