I was thinking same thing escort missions with whomever I may have to escort is way to easily killed. I have even cleared the map and then tried to escort them and new enemy's spawn and kill him very quickly lol  

clear everything before opening the room with the npc usually helps.

or just kill stuff faster ...

not possible to kill everything before since you dont know the time. with the new psyker marines sometimes just impossible. its retarded that they can die. it adds nothing to the game other than frustration because i cannot control nor predict what the npc will do. now we have psyker whole map aoe basically oneshotting vip