Speaking as a BRD, we’re always told to clip our DoTs with IJ at 1~3 seconds remaining, rather than allowing them to drop entirely because of the potency loss. I would think that NINs would follow a similar rule—losing ticks of Shadow Fang may not be enough to offset the potency of an additional Aeolian Edge combo. To be safe, I would personally clip it rather than let it drop, but I guess it depends on the duration remaining when you finish your second AE combo whether you opt for SF or for another AE. I’m not a NIN main though, so someone who mains it would probably be better equipped to give a definitive answer.