Pre layout simulations would not have the resistance and capacitance components to take into account. It helps us to find out if circuit is working functionally.
After you do layout, virtuoso allows you to do a RC extraction which contains the resistance and capacitance values ie the parasitic values. These allow you to figure out if the circuit would work when you actually get the chip done.
Is there a chance the circuit wont work after layout, drc and lvs runs?. Yes its possible. All these just prove that the circuit had been laid out correctly. But due to the effect of resistance and capacitances, there is a chance that some signals get affected and hence the circuit does not behave as expected.
-Aravind