Clark's parents never moved to Metropolis in the show. They visited, and would stay in L&C's guest room in the 4th season (after L&C bought their townhouse) but never left the farm for more than a vacation.
In S5/S6 (one of the fanfic continuations of the show), we had Clark's parents selling the farm in the fifth season in order to travel the world. They would stay with L&C from time to time to help out with the baby. But that was just fanfic -- not canon to the show. If you are setting yours after the show's end, you can do whatever you want with the Kents.
Kathy
