Board Thread:Character Discussion/@comment-24738571-20141001231830/@comment-24674051-20141002184315

I think that, as long as they don't kill the characters off (which I doubt they would do), it would always be possible to bring them back for one or 2 episodes (assuming that the actors want to do it, and the corporate execs ok it).

Of course, as was pointed out, the Frozen characters will be departing after the first arc, so I would not hold my breath for seeing them return.