In my opinion the possibility of death adds necessary(?) tension to the game and brings in another, possibly deeper, level of play.
Players have free will and who am I not to respect that. I just set the stage, it's their turn to get up there and make it shine.
Staying alive, backup plans, etc. are within their responsibility (to a certain degree
![Wink ;)](https://forums.shadowruntabletop.com/Smileys/default/wink.gif)
).
Also, if something goes really wrong that's what Edge is for.
That said, there are (at least) two things to take into account when playing like that.
First of all, the players and me, we all know, that the guy who got some lucky shots last time can get badly betrayed by lady luck next time, so whenever players realize they have to retreat, I won't put extra obstacles in their way as, someone said it before, it's neither a GMs Job to play "against" players nor to kill them when he's got the chance to. I also avoid any "shoot outs" that leave only dead players or dead NPCs - after all it's the players choice how they want to handle a certain situation.
Secondly, should, for whatever reasons, a player get caught up in over his head, I do not force death upon him, so to speak. I let them surrender, or do whatever it takes to survive. So far I haven't come across a single "all in" situation (that wasn't forced by players whom i had previously warned about the possible consequences).
When I get to know my players better (or more so, their new caracters, as we play together for about 10 years now), i of course create situations specifically suited for one particular character that are also tense, in which even the groups life, success etc. lies in the hands of that one character, but they aren't created as 50/50 situations to begin with.
In general there is one particular advice that has helped me tremendously: Be aware of your players current situation and get a feeling for when they can take another hit and when they don't. And if they can't and just want to get out alive - don't go all out on them. Sometimes surviving a run can be as satisfying as dancing with Richard Villiers Daughter while pretending to be an Asian Billionair.
They best GMs I've played with so far, all had a very good feel for their players capabilities and designed their runs, adventures etc. around that skill set (and state of - player - minds). Most situations I've come across so far that got a character killed either came from that character's player not realizing he was in imminent danger of dying should he go on like this, or from the GM not realizing that his players couldn't handle the obstacles he had thrown in his way until it was too late - and not being flexible enough to give his players a way to possibly escape (Even then... who wants to get his as handed only to be saved by the GM?).