But then we got the splainin from the Doctor:
“He gave his life for a friend once. Another friend brought him back.”
From TARDIS - the 'Doctor Who' wiki:
Commander Strax was a Sontaran commander who was demoted to nurse by the Sontaran Empire. He fought and died at the Battle of Demon's Run, as a reimbursement to the Doctor, whom he owed a debt to for saving his life.
Following his death, Strax was brought back to life by a friend of the Doctor's. (TV: The Snowmen)
But we don't learn who that friend was. It could be that this is a minor mystery that will one day be revealed in a future episode of the show. Or it could be one of those little details that will only find splainin in the fevered writings of fanficcers, in much the same way as when Conan Doyle - excuse me, Dr. Watson! - left such tidbits in his stories about Sherlock Holmes, like the Giant Rat of Sumatra and the remarkable worm said to be unknown to science.
I don't have much interest in the circumstances surrounding the debt Strax owed to the Doctor; there were probably hundreds of such people throughout Time and Space. (Although I do like the idea that it was the Eighth Incarnation of the Doctor who first held that debt.) But I'm keen to learn who it was that brought Strax back to life.
When the Doctor says it was a friend, that doesn't mean it has to be limited to the people in his life who could only be found in the televised canon. As a Caretaker of the TV Universe, I say the Doctor came into contact with lots of TV characters from other TV shows, TV movies, and even from TV commercials.
At the end of the Demon's Run battle, the Doctor took off in search of the abducted baby Melody Pond. He left River Song in charge of getting the others - Amy & Rory and Vastra and Jenny - back to their respective times. I think that out of decency River would also have taken the bodies of Strax and of Lorna Bucket, a "Gamma Girl" from the Gamma Forests, who had encountered the Eleventh Incarnation of the Doctor as a young girl.
In recovering the body of Strax, Rory (a nurse by training) might have noticed that Strax was only mostly dead. (Don't worry - we're not crossing over into BookWorld or the Cineverse for a visit with Miracle Max!) And so River Song might have felt compelled to mess with the established events - as she was wont to do - in order to bring the psychotic potato dwarf back to life.
So here's my Super Six List of possible candidates.......
SIX FRIENDS OF THE DOCTOR
WHO COULD HAVE BROUGHT STRAX BACK TO LIFE
River Song could have taken him to Captain Jack (pre-explosion of the Cardiff Torchwood Hub) and asked him to revive the Sontaran with the Resurrection Glove.
So much for staying within the confines of the canon. Nnow we're heading into the outer reaches of Toobworld to explore other options for the resuscitation of Strax.
Dr. Frankenstein knew how to bring the dead back to life, and did so across the Multiverse. He may have been one of those who also owed the Doctor a debt and so was willing to use his reanimation technology on the body of Strax.
Because the crew of the starship Voyager had encountered the parent race of the Sontarans - the Heirarchy - in the Gamma Quadrant, the holographic Doctor might have had the best understanding of the workings of Strax's body, even if it had been "evolved" through centuries of cloning advancements.
At some point, the Doctor could have had a "copy" downloaded into the TARDIS.......
It would have never been a question of refusing treatment to Strax just because the Sontarans had always been hell-bent on conquering the galaxy. "First do no harm" was the tenet that travelled into space with all of the medical advancements, and so Dr. Maxwell and the android nurse Ani would have done all they could to bring Strax back from the brink.
I don't know if the Doctor would have made any kind of deals with the later, harder-edged, archangel. But it was a friend who brought Strax back and later today I'll be making the claim that Castiel did know the Eight Incarnation of the Doctor and even travelled in the TARDIS with him. As an archangel, Castiel would have had the healing powers necessary to create a miracle.....
We know Max could have brought Strax back to life with his alien healing powers. After all, he did so with Liz Parker when she suffered a fatal gunshot wound in the first episode of their series. This set the trials and tribulations of the Roswell refugees into motion. So if he can cure a fatal gunshot wound, fixing a damaged probic vent should be a snap!
The list is limited to six, but here's one last suggestion - Jesus Christ. I would not be surprised if the Doctor and River Song knew Him. The Doctor had been involved with the life of Jesus since before He was born - the Doctor took the last available room in Bethlehem so that Mary had to give birth in the manger. And I wouldn't be surprised if River Song was great pals with Mary Magdalene and through her got the chance to meet the Son of God.......
Strax has come back a little more... stupid (to be as polite as I can) than he was previously, which is why I think he's not the Strax from "A Good Man Goes To War" but instead another middle child from that clone batch of six million.......
Not that I'm complaining, mind. The one-liners from Strax, with his obsession on weaponry as an answer to everything, was a highlight of the episode for me!