I have noticed that not all death in the intro of the game are scripted and some Gf can actually be saved from being killed by Space Pirates. I have tried to search online, but couldn't find a real answer: How many of them can be saved?

Answering my own question and, apparently, it's 9.

3 in the Observation Deck (a bit tricky to save them all and you have to immediately use a missile to save the one who is about to be sliced by a space pirate when you enter; the one on your right when you enter can also easily die if you are not paying attention)

3 in the Courtyard (quite easy to have all 3 of them alive by the time you have cleaned up all space pirates)

And 3 in the Research Lab Zeta (most difficult to pull, you have to get out of the morph ball rails as fast as possible and then go assist as quickly as possible the GF soldier near the entrance of the hangar where you'll have to deal with two space pirate at the same time, but you'll have to start dealing with the 3rd space pirate before even killing those first two, or tat 3rd one will kill an other GF soldier; what matter is that you keep agro-ing the space pirates to tank the damages instead of the GF soldiers)

Also, it looks like the 3 GF soldiers at the landing pad aren't in any risk of dying. And all the other dead GF soldier you encounter were, as far as I know, already dead before you came in.

There is no real reward to save all 9 of them, but it's still a fun challenge, especially on hard mode.

Here is a video about that talk about it (among other things):