Also: is it possible to save a player from every sync-kill? Banshees and Praetorians are easy to rocket while grabbing, Atlases (not frequently do the SK) also give enough time window to pull the Cobra out (pun intended), Scions and Brutes are harder to rocket, because they also sync-kill so rarely that I don't even expect it, and they kill faster, so you have to predict it and press the button just as the animation starts I think. (I don't see many SKs from these three, so I may be wrong here.) The only unit I have never been able to rocket down while instakilling is the Phantom. Is it even possible to do that? There is no lenghty grab animation or anything, it stabs and the player is red nearly instantly. I guess if you already have the Cobra out (sorry), you can prevent it.
Funny you mention this, I came to post my recent high, and it relates 
High: saved a teammate from a phantom sync kill with a superbly timed (read: lucky
) shadow strike. I was cloaked and looking for my next target, saw the phantom slash at and stagger a batarian, who was clearly unaware she was there, and I just knew he was about to be gutted. Pulled the trigger on shadow strike, and got there juuuuuust in the nick of time (the sync animation had started already). Sorry Centurion, the batarian survived the surgery, but I am afraid there wasn't anything we could do to save the phantom 
So yes, it is possible to save a teammate, but you need impeccable timing (again, read: luck), and be aware it is going to happen. I have managed to save someone with SS and lash so far, so I assume a rocket might get the job done as well.