Depends on the situation.
Butt.. I'm going say Blair.
.. & that's all I'm saying because I don't wanna get into this THAT much ;P

Blair would be okay. She'd keep living in her fantasy world where Nate is her prince charming and Serena is the perfect best friend.
However, Chuck has no one to fall back on and would probably feel alone in the world without B.

i dont think blair would be 'okay' in any sence. I think she is well and truly over nate, and i think she is madly in love with chuck. I think if chuck died she would be devestated, but she would have serena. Chuck on the other hand would have lost everyone he truly loves

chuck would have no SL without her ..that would be so miserable !!while Blair will have Nate and Serena and NYU and Blah blah ..lol

Both but I'm going with Blair on this.

He's Chuck Bass. Who wouldn't miserable without him?

I agree with sarabeara! I think Chuck was very unhappy without Blair! :)

he get really upset sometimes if blair is not with him,and he is more happy with her

Blair has the talent to go and live in a fantasy world without interacting a great deal with Chuck.
Chuck when he hasn't been with Blair in the past still lurks in the shadows thinking of her.