The Daleks were not aware that any Thals survived the war as they could not leave their city. The Daleks coundn’t leave the city as it provided the static electricity they needed to operate. The Thals had evolved and adapted to the radiation. Below are some pictures of the Dalek city, the map on the right charts the history of the Thals.
The second time the Doctor saw Skaro was in The Evil of the Daleks. This time the Daleks were controlled by the Emperor that lived in the middle of the new Dalek city.
The Thals and Kaleds were at war with each other, both lived in seperate domes on Skaro. Davros betrayed the Kaleds as they wouldn’t allow him to complete his Daleks. Davros helped the Thals launch a nuclear attack on the Kaled dome wiping out the Kaled race.
A destroyed and presumably abandoned Skaro was shown briefly in Asylum of the Daleks. A Dalek agent had been sent to capture the Doctor and take him to the Parliament of the Daleks spaceship.
SKARO WAS MOST RECENTLY SEEN WHEN DAVROS BROUGHT MANY OLD DALEKS BACK, SUCH AS THE DALEK SUPREME AND THE CULT OF SKARO, IN ORDER TO TRICK THE DOCTOR INTO GIVING HIM SOME OF HIS REGENERATION ENERGY.