W.S.
I have never heard about its repairing. If its damaged / broken, then the only solution is to replace it.
You may check Chah-E-Sultan i.e. Sultan da Khuu, in Rawalpindi.
Check engine light may turn ON, O2 sensor may misbehave and send false readings to the ECU. Fuel consumption may increase. Sound from exhaust may change. Exhaust gases will go unfiltered into the environment, which is "Nainsaafi" with fellow human beings and the environment.