This is what we thought the most plausible reason for his freedom, though it could simply be that Dr. Derevenko was not a courtier. He was very much like a modern doctor, being a businessman as well. And of course, he had not exactly hidden his bitterness over being dragged into exile with the family: Gleb Botkin remembered Derevenko yelling at Dr. Botkin more than once, "Some job you've found for me, I'm telling you!"
We also came across a small piece of testimony from a Bolshevik stating that Dr. Botkin might also have been allowed to leave the Ipatiev House and live at liberty in Ekaterinburg, had some members of the Ural Regional Soviet not taken a dislike to his somewhat high-handed attitude -- or what they perceived as his high-hadned attitude. Although I wonder if Botkin would have left the Ipatiev House voluntarily anyway...
Derevenko has always been a difficult case to read. Some think that he totally went over to the Bolsheviks, "abandoning himself among the enemy" as Mikhail Diterikhs called it. But I tend to believe that he simply tried to do the best he could for the Romanovs, while always placing his own family's well-being first. He was devoted to his mother, wife and Kolya.
Which is not to say that he did not do what he could for the Family from the outside. He may well have been a point-man for monarchist plotters who gathered in the city. There are vague hints that he passed information to Tatishchev and Dolgoruky, who may have been released from prison at one point. Of course, all of this is very nebulous because Tatishchev and Dolgoruky were either killed by the Ural Regional Soviet, or disappeared in the Civil War; Derevenko remained in the Soviet Union, keeping his head down and trying to get on with life; and Kolya was silent on what he may have known, if anything as he was so young at the time.
Now that Nicholas Derevenko is dead, it would be interesting to know if he ever confided anything in his family. I find it easy to believe that he kept his mouth shut in order to protect any family or friends he may still have had in the Soviet Union -- plus I can completely understand his not wanting to expose family business to the public eye. He may also, like his father, have wanted to limit his association with the Imperial Family. But hopefully he will have said a thing or two to his children or grandchildren -- and hopefully, at some time, someone will interview them.