I like the idea of eventually having a squad of rescued marines, each levelled up and armed so as to help out as much as possible. But, awesome factor aside, I have problems with this idea.
Firstly is balance. Things are balanced as they are now. If the survivors can be roughly comparable in power to the player, then the game will become too easy. If they're not, they have no purpose to begin with. Does anyone remember those customised bots in Quake, the ones you could give orders to? They were fun to have around, but made the single player game easier than it already was, and encouraged the player to sit back and watch the bots shoot stuff. The same thing will happen here.
Secondly, and most importantly, is the quality of teammates in roguelikes in general. Despite blurb of 'innovative AI procedures', 'form a bond with your allies' and 'reacts to your actions and learns from them', teammates in roguelikes generally end up with me screaming at them to attack the damned goblins instead of running in circles. They need constant babysitting, are ineffective, and in almost all cases have code put in to make them betray you at the slightest provocation. I tend to shoot so-called friends in the head if doing so won't hurt my alignment. (BTW, thank you Kornel for not putting in alignment systems.) Now imagine this in context of a game where marines can use rocket launchers, blow holes in walls, traipse across lava, and fire shotguns in crowded areas. Do you really want these prodigies following you?