I think it is impossible to lose by such a margin in a T20 match, but the game will be very challenging because after losing the Test series, the desire to win will definitely arise in the minds of the West Indies team players and the possibility of performing well will be the highest.
West Indies are a different team altogether in the T20 format which is why this could be a competitive series considering the fact that it's a 5 match series. I would still give the edge to the Aussies though.
They can acquire some sort of relief after that humiliating test series whitewash if they end up winning this T20 series though.