Question

What happens if we interchange pmos and nmos in a cmos inverter?

Answer 1

When pmos and nmos are interchanged in CMOS inverter it gives a buffer with weak output states.  

If again the PMOS transistor be from Vcc down so when its input goes low it passes and pulls the output high opposite to the NMOS one be at ground so when input goes high then output goes low.

For input 1, the output would be a degraded 1 (as pull-up NMOS is not strong conductor of Logic 1).  

For input 0, output would be a degraded 0 (as the pull-down PMOS is not strong conductor of Logic 0).