Found this and wanted to spread the word:http://steamcommunity.com/sharedfiles/filedetails/?id=326573...
All credit to Carrion at the SteamCommunity forums.
As long as you load your save before you get the black screen with reload options, you have not yet died. Basically, if you see the beginning of a death animation, load your last save immediately.
If you don't load in time, you can "Load Previous Save" to continue from your previous save locations with no deaths.
Update: I've just semi-confirmed that this works; I just got "Hide, Run, Survive" for completing mission 5 without being killed by the alien. I was caught by the alien at least three times, and every time I manually reloaded my current save as the death animation began. Still got the cheevo at the end of the level.
Thus, "death" does not occur unless you allow the animation to complete and you see the reload screen.
Update 2: Further confirmed by gaining the achievement for completing the hive level without dying, despite being caught several times.
If, when you are loading your save, you see "Resume Game" as your first menu option, you're in the clear. If the first menu option is "Load Current Save," you are too late, and should reload your previous save.
And, if you're still uncertain, there's always "Load Mission Save."
Again, all credit to Carrion at steamcommunity.com