Exhaust Problem...

I was driving down the highway going about 70 when i saw what looked to be a catalytic converter laying in the middle of my lane (far left). I couldn't get over to the right (semi) and it was heavy traffic, so i tried to slow down and make sure it went between the tires... I felt a little bump and heard something hit.... :banghead:

I looked under the car the next day after i turned the engine on and now i see "gas/air" coming out from the joint connecting the catalytic converter to the rest of the exhaust work. Is this a serious problem? :sly: How much would an exhaust job be if i were to replace everything after the cc?

Thanks in advance...