So cait sith is a familiar, a cursed cat-thing granted sentience by its master. Very much like the poroggos in Dravanian hinterlands does cait sith share several similarities including but not limited to: Magical abilities, Animal shape, humanoid-ish pose etc.
However, the poroggos seem to have gone somewhat feral. At least those without masters. It is about 15 years since the settlement was evacuated.
Cait Sith has kept its sentience for 1500 years without a master. Shouldnt the cat have returned to its animal form without an active master to keep it sentient?