The proof would have to be very convincing. Although I'm not an expert here (and maybe I'm talking a load of rubbish) as I understand it, even more distant members of the same family would have a similar DNA profile, I mean to say, was the DNA from Prince Philip not used in tests on the Romanov remains and he is hardly what one would describe as an "immediate" relative. Therefore, while someone could have a similar (or matching ?? I'm unsure of these terms) DNA to Nicholas II, it would not automatically mean that he/she was a descend of a child of the last Tsar....he/she could equally be a grand-nephew or fourth cousin or something. I stand open to correction on this, as I'm no expert. However, I find it very difficult to imagine that anyone survived that cellar. I accept that anything is possible, but it would take a great deal to convince me.