Dortmund are shooting themselves in the foot as far as making a profit off their young star, which is the bread and butter of their club. Make no bones about it, they are a selling club who is happy to get an ROI for their players, it's part of their environment. Reyna, Haaland, etc. are next after Sancho. Hakimi, the same thing.
The time to sell Sancho is now for max profit and major cash injections. We all can see that the next domestic season will not have fans. So that's a loss revenue of 17 domestic home matches, x amount of domestic cups, and x amount of CL/EL home matches.
Matchdays are the consistent flow of cash every month. Sponsorship dollars are usually 3 times per year or some quarterly payment cadence, not included year end performance bonuses. Even then, those bonuses could be spread across months or payment installments.
All this to say is that Dortmund will lose Sancho, not if, but when. It'd be a poor financial decision if they let his contract go down another window or year because they will not be able to command a higher fee. They can still be a good team semi-challenging Bayern and finishing in a CL spot without Sancho. They can play hardball all they want, but if this window passes and he's still on their books, good for them and their pride, but bad asset management in terms of revenue at a time and the foreseeable future where having money and cash is extremely, extremely important for football clubs.