Canon reviews might stop a muse from fading but sometimes the reason why a muse fade is because you, the player, want them to fade.

I.e. Look at what happened to my Balthier-muse I used to have. He is utterly dead while my Noah(Gabranth)-muse is still alive despite the fact they are from the same canon.

Sometimes we subconsciously want to let go of muses that we feel in someway do not fit us well.