The bundesliga may likely not get much attention from Dortmund this period and so they may want to rest players because achieving the champions league will actually means a whole lot to them as they are going to even gain more game in the fact that they were able to win the champions league so they may actually not mind resting players for the champions league an this may actually affect their performance in the bundesliga.
But if that is done then indeed it will have an impact on the competitive situation in the race for the Champions League next season.
It should be noted that their current position is still unfavorable and if indeed they release the Bundesliga for the rest of the season then the worst possibility is that they must prepare not to compete in the Champions League next season.
Although their chance to qualify automatically can still happen when they win the Champions League this season but it is clearly very difficult. Their semi-final will be against PSG and even if they win in the final they will face one of the clubs from Madrid or Bayern so their chance of automatic qualification is difficult and rather than expecting that it would be better if they continue to strive until the end to compete and try to take 4th place in the standings from Leipzig in order to feel comfortable to be in the Champions League competition next season.