I agree that Nicholas himself would not have been able to save the throne for the Romanovs. But he could have given others the power to do so. Witte and Stolypin were very successful until Nicholas lost confidence in them. When Nicholas felt they threatened his powers, they fell out of favor. But with a good team around him and enough mutual trust they could have come a long way.
Maybe yes, maybe no. I think the political situation in early 20th-century imperial Russia was dicey, dodgy, in plain and simple terms, terribly tricky. One major problem with Stolypin was that he was not a good team player, in fact he tended to be somewhat autocratic in his own methods, so he alienated a lot of potential supporters in the political field and thus ultimately failed to build a real power base that could keep him alive as a political player in the event that he fell out of Nicholas II's favor. Which is why, when Nicholas II turned away from him, Stolypin didn't have a leg left to stand on and was fading so quickly from the political scene when he was assassinated.
It's also a point of much debate among historians of this period whether Stolypin's reforms had been moderately successful or an overall failure. One thing you're not taking into account is the Russian peasantry, which virtually every member of the educated elite (partly in reaction to the horrors of the Revolution of 1905-06) saw as a real hindrance to modernization and liberalization in Russia. This is very much reflected in authors of the period - Gorky (who himself came from the lower classes) despised the peasantry, and Chekhov wrote several stories in which Russian peasants are remarkable chiefly for their backwardness. So it's not remarkable if Stolypin's reforms were a failure, especially since a large segment of the peasantry were apparently opposed to them.
I don't know enough about Witte to make a judgment on him.