At first, I thought there must be intentions of bringing her back, as there were constant references to her in Series 3, as if the writers wanted to keep her fresh in our minds for when she did return.
But when I really thought about it, this is a childrens show at heart and they need to affirm that the character is not dead or trapped but has just moved on. Unlike the Doctor who has had to move on from Rose and the like, Luke and Clyde as children have the luxury of security where the writers are concerned.
But who knows, she could one day make a comeback. I feel it would be out of place though unless handled very well.