The engine is a small part of what makes the game great. The dialogue and little details are what made it great, and those will be difficult for other people to create, partiularly if they're focused on the gameplay.
“That’s not what we were made for,” Vincke said. “That’s literally the opposite of what Larian is about. We want to do big, new things. We don’t want to rehash the thing that we’ve done already.”
That's great, but I'd bet good money their next game will be DOS 3, which would not be a "new thing" I think more likely they don't want to have to kick back that $90,000,000 to Hasbro and think they have enough reputation to go it alone, which they might. But the Divinity games just didn't resound with me like this one did, so it will be a net loss to me personally