I'm not familiar enough with licensing contracts of this nature to know whether there are royalties being paid out based on the number of copies being sold. But in the case of whether WotC is going to get paid again for another licensed Baldur's Gate game in the future, that's already a done deal. Sales from this point aren't going to matter. It's similar to how that became clear pretty quick in the case of Hogwarts Legacy.

D&D is among the most mature IPs in gaming. It's not going anywhere, and Hasbro has it right now. The most effective thing you can do is support one of its competitors, like Paizo's Pathfinder.

As for whether you should pirate it, something to weigh is that Larian is one of the good guys. This is an offline/single-player capable game, with no MTX.