Nothing in particular about the Sixth Calamity is relevant to the Void, save that voidsent were involved, most notably Diabolos. Who was killed for good back in Dun Scaith. There is, quite frankly, no reason for that to be brought up now. Mhach hasn't been mentioned for the same reason; it simply has nothing to do with the current story. We might as well be wondering what the Lambs of Dalamud have been up to lately.