Do you want to bet that the final price will not be €120m guaranteed, if you are so confident?
I don't bet with strangers on the internet
But you seem to think I'm just a Bundesliga fan boy. I may be, but I have really put some thoughts into this since we are in a similar situation with Havertz and Chelsea. Thing is, this is a unique economic situation because of Corona. In a regular market it makes total sense to sell your players two years before their contracts run out. But in this case, there are two factors that work against that:
1) The market next year will have recovered by at least a considerable margin. This means that prices will rise again. It may very well be the case that Dortmund can sell Sancho for only 10-20m less than what the top bidder (apparently you) is offering this season. That deprives the scenario that Sancho stays for another year of its terror.
2) Why is selling in the last contract year such an uncomfortable bargaining position for the selling club to begin with? Because the buyer can threaten to sign the player next season when his contract has run out for free. But therefore the player
has to be willing to let his contract run out in the first place. Sancho already wanted to leave last season, he's eager to leave this one. You or whoever else would be trying to sign him next season would have to convince him of the general possibility to stay for an additional year, meaning that he would make the step to a top club four years (!) after his initial intention. That won't happen, he'll want to leave immediately and Dortmund knows this. This makes the "take the money or we'll wait another year and sign him as a free agent" threat a hollow one. If one club meets Dortmund's demands, he'll go there, even if he'd generally prefer another team. He won't wait. From this point onward, it becomes a game theory situation. All interested parties would have to stick to the implicit agreement to not pay the actual market price with only one year left on the contract. However, one club does that and the player will go there. So you can be dead sure that one club in a recovered economic situation will want to secure the signature of arguably the most promising youngster in the world.
I mean, imagine the situation that you guys, Liverpool, Real, Barcelona, PSG, Chelsea and Juve are interested. Dortmund asks for 100m although there's only one year left on the contract. Sancho would prefer United but is totally willing to leave since he doesn't want to waste another year at a club below his level. You guys are hesitant to pay 100m for a player that would be a free agent in one year's time but Barcelona and PSG decide to break the bank and meet Dortmund's demands - do you think he wouldn't go there but stay another year at Dortmund (as I said, 4 years longer than he intended) to go to Manchester? I don't. And yes, you could argue that PSG and Barca would have overpaid but on the other hand, they would've secured the signature of a potential Ballon D'Or winner for 100m which is still a reasonable price in a post-Corona market - a deal that would prove to be a very, very good long term decision since they can sell him for more or profit from it for almost a decade.