For some reason, many people doing Shirataki over again may be able to skip going to fight the miniboss to get the key. Everything else you still have do to over again. Wavebringer isn't like the oni where you just walk into the temple and lo, there he is.
That said a lot of young wizards have to do this more than once, both for the quest and for their spells. Hang out and offer to help.
