question about terminals at PEK

Do all Air China operated flights arrive and depart from terminal 3?

Also, I'm planning to meet a friend in PEK and we both are connecting to the same Air China Flight to Bangkok. What if his flight is on time, but mine is not, or vice versa. What do you recommend we do? Should he not catch the flight and wait for me to catch the flight to Bangkok? Should he board without me, and I'll have to just get there when I can? Will missing the flight on purpose to wait for a friend cost extra money or would they accommadate?