If you have 1 card remaining in your Deck and you activate “Diamond-Dust Cyclone”, selecting a monster with 8 Fog Counters, when the selected monster is destroyed you will lose the Duel because you have to draw 2 cards but you only have 1 card remaining in your Deck.
“Diamond-Dust Cyclone” cannot be activated while there are no cards remaining in your Deck.
If “Diamond-Dust Cyclone” fails to destroy the selected monster (because the monster was removed from the field, etc.), you will not draw card(s) from your Deck.
If you select a monster with “Diamond-Dust Cyclone” and the selected monster is flipped face-down in chain, the monster will still be destroyed but you will not draw any card(s) because the Fog Counters are removed when the selected monster is flipped face-down.