His point is that the scientific premise of this is flawed. We can debate this, he is just saying that the OP is a flawed scenario.
first, it's spelled Romanov. Second, I am fairly sure they were not i Moscow at the time. Unfortunatly, I cannot find my sources; but I think it is more reasonable to assume that they are in St. Petersburg, or on a yacht, or in a dacha on the Black Sea, or in any number of equally probable places, then it is to assume that they are in Moscow at this given time. Do you have any sources to back up your claim? Third, the entire line of succession is not going to be gone. Not everybody is going to die, even if Nicholas, Alexi, Grand Duke Michael, and others perish. Fourth, why is Stalin relavent? He is, while not a nobody, deffinatly not a major force to be reckoned with in Russia, or even the Communist party. At this point in time, even Lenin is a fairly minor figure in the socialist movement. In 1907, he was robbing banks, and in April 1908 he was arrested by the Okhrana, and thus removed from play. Russia will be devastated by this event, Stalin is almost certainly butterflied out of existence.