Assuming that the baby is his, I think that Chuck will be happy. Chuck truly loves Blair, and he's grown up so much as a character. I also think that he'll be a little nervous and a little più protective of Blair if she happens to be pregnant. Ultimately, though, I'm pretty sure he will Amore that baby with all of his heart. <3
If it had happened in season 1, 2, 3 o early 4... I don't think he would have reacted well, probarly requested Blair to get an about o something like that... But in the end of season 4, he seemed to have grown up as Chuck have detto himself :)... So I believe he'll be happy <3
So I'm hoping she IS pregnant, which I'm pretty sure she is, after I've seen one of the shoots! :D
I think he will be like OMG, but then he will think okay now I have a future with the person I Amore the most (Blair) and going to have a family. And I think that's what Chuck really needs: a family..