The sad thing is any significant profit-share with WotC, assuming there is one, makes sequels or even expansions for BG3 less likely.
BG3 has elevated Larian to "full AAA" status, with over 400 employees, and unless it's bad in shocking and unexpected ways (seems unlikely, at this point), they will be huge news in PC gaming and RPGs especially. Plus they're independent and not IPO'd. It's very likely they'll get some fairly bonkers acquisition offers (Hasbro WotC probably can't afford them, though).
If they want to stay independent and successful, their smartest move is probably like that of Bioware, to create an original fantasy IP, and rely on people buying it because "It's Larian!" rather than relying on people buying it because "It's D&D" or "It's Baldur's Gate". That's why Dragon Age was created. WotC didn't necessarily want a huge cut from D&D games, and weren't too bad re: interfering (unlike say, Games Workshop), but still, D&D was fundamentally their IP, which they could pull or licence to others (even with a contract, it's not going to be indefinite - you could make a successful game and WotC could say no to a sequel), and even if they didn't, and Bioware did an amazing job, they're both having to either pay a licence fee, or give away a cut, and are boosting an IP that isn't theirs.
I suspect they won't go back to DOS' setting because it's a rather dull and generic setting, even by fantasy setting standards (which are very low).