I think Nicholas and Alexandra's general unfitness to be Tsar and Tsarina hastened the fall of the House of Romanov, but I think it was coming anyway and had been for a long time. I'm not sure any autocract on the throne during WWI in Russia could have survived.
To me the saddest thing about N and A is how thoroughly the deck was stacked against them from day one--from Alexander III failing to properly educate or prepare his son, Nicholas's own weak willed personality, his domineering uncles (who often-though not always-gave poor advice), Alexandra's shyness, dominating personality, inflexibility, her own mother-in-law publicly working against her, her complete lack of preparation to go from a small modest court to the lavish, immodest Russsian one.....True, neither one ever "rose to the occassion"....but the whole situation is just incredibly sad to me. I just don't think either one of them really knew what they were doing.
I'm not an expert, but I tend to think the last real chance to save the institution was when Alexander II was Tsar and was instituting his reforms, including a constitution. Had he not been assassinated and lived long enough to get his reforms firmly in place.....maybe things would have been different. Even then, that may have been "too little, too late." Beyond that, if Nicholas II had been serious about giving the people more of a voice after the 1905 Revolution....perhaps. But, he wasn't. He thought he was supposed to be an autocrat.