Your logic will only apply if they don't get CL football but with it they are still in a strong position to keep him or sell only for a premium fee BVB are a selling club but not as desperate as people think. Their project is worth more than the profits hence why they sold Dembele for 150m even when he handed in a transfer request and why they were firm on Sancho and speaking of Sancho he's leaving this summer and as
@Zehner told me last summer BVB are all about PR it'll be disastrous for them to sell both their stars in the same summer so unless a catastrophic financial disaster happens they'll sell Sancho and keep Haaland till 2022
Last year the situation was like this: Everybody assumed Sancho would leave. Few BVB fans had hopes he'd stay over the summer. Then Dortmund communicated the deadline (and in Germany, everybody took that seriously) and dropped the Sancho extension bomb, the deadline passed and the BVB communicated he's staying. It would've seemed as if the BVB leadership toyed with the club's fans for no reason at all if he left after this. And especially since they're so desperate to draw levels with the other big European clubs, it would've fed certain inferiority complexes ("selling club", "local phenomenon and no global player", narratives like that) they have had at the very least since the Götze departure to Bayern. Expectations are the key word: They've communicated this so clearly that there was no going back from it.
Anyway, that was last year and right now I think the situation is very hard to judge. If you ask most fans, they expect a Sancho departure this year and a Haaland one next year but also have hopes of seeing them together for another season. It's uncertain, primarily because there are no public statements or anything like that. Right now everything is possible. I could imagine that both players are going to leave but also that both are staying. I could imagine that Dortmund are willing to accept smaller fees as well as them demanding a similar amount to last year, without any Corona discount. I can also imagine that there are no interests at all since the players are just too expensive in the current environent. And then there's also the possibility that the players deem no offer interesting enough, either monetarily or ambition-wise. This could even lead to Sancho extending for another year for higher salaries, especially if Haaland stays and Rose leaves a good first impression on him.
It's just too early. Once summer is here and the rumors start becoming to most relevant topics again, let's see what happens.