In closed loop configuration of op-amp,what happens to open loop gain?
The open loop gain does not change.  

The feedback drives the difference between the + and - terminals to a very small value such that the small value times the open loop gain is the correct output voltage for the closed-loop topology.



In the picture above, the closed loop gain is -R2/R1.  So the feedback causes the voltage across RIN to be whatever value is needed to give that closed loop gain when multiplied by the large gain "A".