Bioware is good at making ridiculous amounts of content as far as characters go. Every possible combination of things from the first two games will be included. Like the rachni queen sending you the messenger if you chose that branch of quest in the first game. Every combo of content will be included, the only characters that will "disappear" are the ones that died, horrible random chance deaths. If you kept everybody alive, you probably lose some to the typical "I'm gonna gather your army, see ya", but they have to keep others... they might even make it a choice in itself, and get you to pick who leaves your side to gather the forces. Choosing the cool characters that you've really liked, might end up making the endgame more difficult, because they may have gathered the coolest of the available dudes... My inner strategy and quest chain nerd is suddenly hopeful.