With the masses of deals between certain city pairs I was wondering what happens in the below circumstance.

For instance
If I fly between a to b on (x airline)
Then b to c on (y airline)
C to b ( y airline)
And then b to a (x airline)

And book ticket through a third party would the no show rule not apply ie I could then skip the x airline flights and only take the y airline flights which is more beneficial to me without risking cancelling all flights?

Thoughts?