So let's just entertain the possibility of Dortmund going down (personally I don't think they will - teams a la Werder and Berlin are guaranteed to fvck up and let Dortmund escape, not Stuttgart though, they always, always,
have a super second half of the season), who would stay in the team? Let's see:
Klopp: hard to call. If he isn't sacked midway through the season, then he probably won't in the summer either. And his stock wouldn't increase so suitors from abroad wouldn't be plentiful either. I think it all depends on how the campaign goes - if Dortmund get better and only barely get relegated in the end, then he really could stay on, but if he fails to pick up more than 2-3 points from the next 9 games, he's out, surely?
Weidenfehler: belongs in the 2. Liga.
Hummels: dude's out, no question about it. At the moment in his career where he'll make the step towards his top form, he cannot allow a year in the lower leagues. The only question is where, as he'll have his pick considering Dortmund will be financially certain to accept most bids.
Subotic: Also belongs in the 2. Liga. Probably has an inflated opinion of himself so leaving for a mid-lower-table club in a top league would fall through.
Papa: Now he is interesting. Doesn't have the high reputation of the former two, so suitors from abroad could be sparse. Joining a Gladbach or Wolfsburg would be ideal, but Dortmund will want to keep on one of their top class players when possible.
Schmelzer: who cares?
Durm: Probably still young and impressionable enough to stay with ol Kloppo in the 2. Liga, if he's still there.
Piszczek: Only one year remaining on his deal this summer, so... could keep his options open in case Dortmund manage an instant promotion. Isn't glamorous enough for big foreign interest.
Sahin: Kid knows better than to leave Dortmund.
Sven Bender: Another player who really can't afford a year away from the top division (much less a guaranteed two year stay away from european football). Despite not being a "big" name, he really should be on his way out when relegated. Back to München...?
Gündogan: His injury makes things complicated - otherwise he'd be out the moment anyone comes sniffing. All depends on interest in him - he'll surely love to switch clubs, but his stock may be down after the injury problems.
Reus: Out even if they don't
Aubameyang: Curious this. Surely didn't leave Saint-Etienne to play in the 2. Liga, but will probably be on some decent wages and convinced that Dortmund will make an instant recovery. Besides, a pacy player like him could tear the lower league apart.
Miki: Do Dortmund even want him? How his worth has dropped.
Immobile: I wonder if he will be scapegoated for relegation? Could be... I'm sure some mid-table Italian side will come in with a low-ball bid to find it accepted and Immobile once again scoring 20+ goals in Serie A.
Kampl: Only just joined - both sides probably wouldn't yet want him moving.
Adrian Ramos: Perfect striker for the 2. Liga - and not prestigious enough to attract bids from top teams. Will surely stay.
BONUS - Grosskreutz: Belongs in the 3. Liga.