The only level I believe Dortmund are not going to fall is their relegation but anything outside that they don't have a limitation, so actually I think they will fall a little more because of what they have to faced, so the few matches you said is what will justify it. Augsburg which is led by Jess Thorup can make his team to resist Borussia Dortmund since the both has the same to loss, however is a club with higher prestige Augsburg usually knell down, though they have not done it to Leverkusen but Borussia M'gladbach got it two match ago from Augsburg 3:0. However I have Freiburg on mind to also win Borussia Dortmund along the way.
They won't even come close to relegation because the team on 16th position has 18 points less compared to Dortmund, they won't even reach BVB's 35 points this season, most likely not even close. So nobody should even mention Dortmund and relegation in 1 sentence, cause it's basically impossible to happen.
If they get their shit together they can still reach Europe, but that's a tough task of course. After some winnable games there will be a barrage of top teams waiting for them.
For relegation, Borussia Dortmund are already safe from there because the gap is enough to make them safe, because it is impossible for them to lose all the remaining games. But even so, the position they are in now is still a bad position and I don't even remember after completing 24 games whether they have ever been in that position or not. 6 points is their distance from the club in 4th position in the standings, they can still catch up, yes, although it will be quite difficult. It would be amazing if they managed to reach that position at the end of the season.