Bingo.
Pulisic was 'smart' to just extend until 2020 to have all options open short-term. If he really wishes to leave, then Dortmund cannot do too much with just 2 years of contract left at the end of the season. They will fight tooth and nail though to keep him at least until 2019 trying to extend and it will be extremely tough to convince them to negotiate a sale. They will be max stubborn in that case trying to avoid a pattern at all costs.
Pulisic is no Dembele though and I highly doubt, that he would try to force a move away that way. The most likely scenario IMO here is another extension prob until 2021 or hopefully 2022. I think he doesnt want to move to another club..yet.
Dortmund will try to sell Aubameyang for around 80m€ and trying to keep their promising youngsters. IMO they should get rid off Bosz first and then the wannabe leaders Sahin, Schmelzer, Castro & Co. next. Rode, Schürrle, Sokrates and some others should be sold too..too much mediocrity there, so time to reshape.