It's most likely a standalone self-contained story like Season of Storms, so I don't think it will have any major impact
As for influencing the story, there was a similar situation with Witcher 3. The game was already in development when Season of Storms was released. While the main game didn't had references to it, DLCs had references to some of the plot threads from that book (Borsodi's auction house in Hearts of Stone, etc). It'll probably be a similar case
I don't think Sapkowski is interested in tieing this to games tbh