We'll see how far Dortmund will push him and Chelsea, but as it stands, they haven't even given any indication to the public that there's even a condition where they will sell Haaland.
Yeah, I can see the different between the release clause and a potential offer being too good for Dortmund. If that was the case, then wouldn't Watzke have given out hints indicating this? Last summer, with Sancho, he was very clear about a possible sale. With Haaland, however, he's been the exact opposite.
Regardless, we haven't seen them linked to any new strikers. Last summer, when Sancho was leaving, Dortmund was getting linked to several players who they were monitoring, with Ikoné being one of them. This summer, however, I've yet to read about them being linked to a striker from more reliable sources (in or outside of Germany). Does that not give us an idea of Dortmund's plans for next season (i.e. keep Haaland)? Maybe in the next few days/weeks, we'll see more stories come out depending on how Chelsea's talks fare (with Haaland's camp, mainly).