Uhhh I don't know why so many people think Wakaindashi won't get performed later. It definitely is not going to end with Duu's graduation. I translated the notes from Tsunku a few weeks back and he definitely hinted this song will be performed a lot in the future.
It is Kudou's graduation support song but it also ties in well with Morning Musume's live performances and their encores and I have a hunch that this song can go on to be established as a song for many places where the girls cry and laugh at the same time.