I don't think Haaland will continue in the Bundesliga. If so, he will not leave Dortmund. He is more likely to go to another league, another team. My guess is Real Madrid can buy him. Benzema's seasons not long now. Haaland is a quality striker who can play for many years in Real. I also heard that Haaland wanted to play for Real Madrid.
The pressure on Haaland in Dormund is much. They depends on his mostly in scoring goals. It won't be a bad ideal if he goes to another team, it will probably help as it will introduce him to new challenges, while he will further his career. Real Madrid won't be a bad choice, he will link up with Benzema, and also strengthen their squad. But I prefer his play in Manchester City, where he will spend more time playing in Champions League. But, if Haaland eventually leaves Dormund, it will surely affect them , as his is presently their goal machine.
I also believe that Haaland in the Spanish or the English league will be improving better than in Bundesliga. Borussia Dortmund certainly realizes that if they lose him, they will have big problems next season. Borussia's problems may be even greater if it turns out that Bayern Munich will win the contract with Haaland.