First, a few points to note:
1) Russia had a monarch as late as 1917, more recently than France (1871).
2) The Russian Revolution, with particular reference to the Nicholas II’s immediate family, was far more violent. He was shot alongside his son in 1918, a month after his brother Michael, who had no legitimate son.
3) From about 1800, Russia adopted a semi-Salic Law, thereby emulating France, so that Catherine the Great was the last female Tsar, unless no male relatives are available. We must also be careful to exclude those descended from morganatic (unequal or non-royal) marriages and we must be sure that the answer is a follower of the Russian Orthodox faith.
We are, therefore, almost certainly looking for a male claimant in the same male line as Nicholas II. His other two brothers died without issue.
Anyway, here is their answer. The hypothetical Tsar of Russia is: Grand Duchess Mariya, granddaughter of Grand Duke Kyrill Vladimirovitch, first cousin to Nicholas. She would qualify despite the Pauline rules because the Russian and Georgian monarchies, among others, ceased to rule in 1917 and the objection to morganatic marriages couldn’t apply. She has a son and grandchildren.
Otherwise, there was an Andrew, strictly in the male line, who died in late November at 98, but left three sons.