Pound is falling because of statement by Mark Carney. He was against Brexit during the campaign and was proved wrong then in his forecasts. Not the most brilliant of brains, really. He may possibly be trying to talk Brexit down and hope for a self-fulfilling prophecy? Who knows his motives? Why should the 'no deal' option change? It seems to me to be the better bet right now.
"No deal" is never the better option, and anyone who thinks it is needs a serious reality check.
As to the pound falling -- don't blame it on Carney, it had fallen long before he said anything, and anyway there's also Liam Fox's warning that no deal was more likely now (warning, note, not promise!). Then there are factors that have nothing to do with Brexit, such as the strengthening of the dollar lately.