Real talk: How crucial would Shelby and Shaw have been for a Star Trek: Picard spinoff?
The crucial thing is selling an idea for a show to the people who make the decisions about which series to develop, pick up for series or pass up. I do think there will probably be a Picard Spinoff, but it might be a while before anything happens.
I mean, the deaths are easy enough to confirm if they've seen screeners up to ep10, but why would yon YouTuber have solid knowledge about what's on the slate?
I doubt they have any solid info about what those in charge of Star Trek are planning. They might have some unconfirmed rumours and are making assumptions.
I think the more likely scenario is that after their near extinction at the hands of Admiral Janeway the Queen learns that Picard had a son and realized what the genetic alterations done to him could mean being passed down to a child.
Maybe the Queen learned that Picard had a son from assimilating Admiral Janeway, she traveled back in time from 2404.
It's either something the Borg Queen stumbled upon or she's always had the knowledge and had no use for it, until Janeway wrecked the Queen's control of the Hive Mind. Maybe Jack is the way around the pathogen Janeway used. It just looks like a more subtle version of the plan the Borg had in Voyager for seeding Earth with a nano probe virus.
Will this be the end of the Borg? I think it might be a question that's left open ended.