1) You would get better responses if you posted this in the perrifels section, not the iMac
2) being under warranty is not relevant you dropped it!!! The warranty covers manufacturing defects only
3) It is possible they may swap it but unlikely.
4) maybe if it stopped working the would replace it but it is still working for peets sake!
Thats like going to a car dealership and asking them to give you a new car after you crashed it.