If Dortmund want to stay competitive with Bayern then selling Guirassy would be the wrong decision, Guirassy has been a huge help in terms of goal productivity for Dortmund over the last two seasons, but I wouldn't be surprised if they sold the player either, especially if there was a high bid, Dortmund wouldn't hesitate, we know how they do business.
By now, we should be able to know that Borussia Dortmund is not a title contending team, they're just here to make more money for themselves by selling their outstanding players, that have been the structure of business for the club. This is no new thing and they have been doing it every season, this is what Borussia Dortmund is known for, selling players making quite good amount of money from them.
You do know borrusia Dortmund is more like Ma lasia where they groom players with values and they groomed them for the bigger clubs, I mean competitive teams who will open bids with this players and become more promising because winning is very necessary for them.