I feel like you guys are mainly basing this on some of the bigger series lasting really long.
Bleach lasted a long time despite a sales drop, and we found out that it only ended due to Tite Kubo’s health.
And then their are some series that like Kochikame and Gintama that had consistent sales, but weren’t MEGA sellers(at least not in their later years), and I’m pretty sure both of those would still be in the magazine if the mangaka wanted them to.
As long as MHA and Black Clover keep their current sales, or don’t drop to the degree that they’re flopping, I feel like they’ll run as long as the mangaka wants them, even if that means moving to another magazine in the later years. If the series is still profitable, and still bringing fans to the magazine, Shuiesha/Jump have no reason to can it if the mangaka still want to keep making it.
Are we really bringing in Kochikame? Kochikame was the front runner for WSJ for almost 3 decades. It was as important as One Piece. Kochikame WAS WSJ's history. It's why it's one of only two series to ever get a cover for its ending in WSJ.
Gintama was a comedy. It sold 55 million volumes while it was majorly known for its comedy. It's volume sales were remarkable for a comedy. And that's besides the remarkably successful media franchise it had.
Bleach sold 120 million worldwide, had an anime that ran for 366 episodes, 4 anime movies, numerous games, merchandise etc. etc. etc. When Bleach entered it's final arc in 2012, its volumes sold 670k ish. There was no reason for WSJ to make it rush to a finish. It was one of their most significant names and they showed the last arc the love especially when they gave the last arc's first chapter a cover and a 5 page extended color. Even the last volume of Bleach sold between 450-500k (Or more. I'm too lazy to look).
Now lets look at Toriko.
Toriko highest print number was 580k at its peak (or somewhere around that number) and it ended within two years of its anime ending. Why? WSJ barely had a series aside from MHA and a new BC with a declining HQ. There was no reason for WSJ to cancel a series that was still selling around 250-300k (a number BC sells at its peak).
Beelzebub sold 150k to 200k towards its end from a 300k-350k peak (similar to BC levels) and was rushed to end.
I'm not hating on BC. I'm simply stating that we have a well documented history of WSJ cancelling major series that were past their prime and had declined in sales. It's why I said, if BC's sales start to decline, it wouldn't last more than 2 years. It's not a wrong assumption at all. Given WSJ's history, it's the right one to make.
You can keep saying it's "not the same WSJ right now" but that would just be a baseless statement. WSJ has always been strict and harsh when it comes to cancelling series even with decent sales. There won't be exceptions. If there has to be an exception for this generation, it will be MHA but definitely won't be BC.