Persimmons (Diospyros kaki) will continue to ripen off the tree as long they turned color on the tree. Ripe Fuyu's are uniformly orange-red. Some varieties are only edible once they soften, but Fuyu's remain firm when they are ripe. Have you tasted any? You may find that they are ready to eat right now! Otherwise, there are no special requirements for ripening-just leave them out at room temperature.
I wasn't able to find research that described what happens to the fruit when they freeze on the tree. However, Fuyu persimmons are known to be sensitive to chilling injury when exposed to cool and freezing temperatures after they are harvested. If your persimmons were damaged, you will see darker-colored and soften areas in the flesh when you cut it open. Click here for a picture of what this could look like. This damage will take at least a few days to develop. You can always cut out the damaged areas if it is small and still use the rest of the fruit.
Hope this helps and thanks for using Ask An Expert!