Star Wars: Rogue One Trailer - 13 Major Plot Hints
4. There's A Lot Of Cannon Fodder

However you look at it, the signs are not good for the other members of Rogue One. They face insurmountable odds and an enemy at the absolute height of its power (even with those shoddy stormtroopers) and they're on a suicide mission with very little hop of success.
Unfortunately for them, the mission is a success. That particularly resolution has been robbed from the audience by the events of A New Hope, so the impetus now is on selling the drama in a different way and still packing a massive punch despite the fact that we all know the end.
The easiest way to do that is to make sure the journey is incredibly fraught, and to kill off the majority of the cast and a massive swathe of the Rebels on their attempts to steal the Death Star plans. There's already a suggestion that the first attempt goes awry and the initial Rogue One squadron are decimated, forcing Jyn to build her own team of bad-ass loners, and frankly the fact that they aren't around for A New Hope suggests they're probably not long for this world.