Nice post.
I think United have the upper hand in this negotiation by stalling. I wonder how much cash reserves of Dortmund is being drawn by this time since March. I wouldn't be surprised if they are currently drawing on their credit line already. The touted 60M upfront may be coincidental but sounds like a figure to ensure their credit continues revolving. Of course, if Dortmund could secure new funding they may be able to strengthen their position, but with the prospect of close stadiums, which bank is going to finance them? Plus if they indeed offer Sancho higher wages, their cash position weakens and potentially disrupts the wage structure at the club.
The point is that Dortmund needs to stay afloat more than United need Sancho. He may be the best winger for our current needs but there are potentially cheaper alternatives, don't ask me to name who but I find it extremely implausible that only Sancho can improve us. All the noise if coming from Dortmund end, and in this situation the more noise they make, it becomes more apparent that their hand is weaker.
I think the right tactic here is to stall and negotiate to sign other alternatives. Dortmund's cash position weakens they longer they remain stubborn. Let's bleed them out.