Many Goldfinches have left north Texas by now, but some remain here. They'll head north sometime soon, and return again next fall. My advice is to leave your thistle (or "nyger") feeder up a little longer to let these stragglers eat. Hang a feeder next to it filled with sunflower seed (I prefer black-oil sunflower). The remaining Goldfinches will always have something to eat; sunflower if and when the thistle is gone; and our year-'round birds (Cardinals, Chickadees etc.) will continue to eat sunflower too.
Incidentally, the small black seed known as thistle (or "Nyger") is the only birdseed that does not stay viable for the following year.