title. is there a command to check if someone is alive, for example?

You could make a script that changes a variable when the NPC is killed. I'm only just looking into scripting for the first time though.

GetDead or GetDeadCount. The Dead Count is more for if you have multiple copies of the same creature in the game and the player needs to kill a certain amount. For just one NPC, use GetDead and the NPC's reference ID. http://geck.gamesas.com/index.php/GetDead

Thank you very much both of you, will experiment with this later!

sorry, where exactly do I put this? I want a dialogue option to only be available once the target is dead

In the conditions for the line of dialog that you want it to affect. Right click in the condition box and say New. They select GetDead, and select your NPC's ref. Then says == 1. That should make the dialog only pop up when the NPC is dead.

ahhhhhhhh! thank you very much !

everyone in goodsprings immediately rushes off to kill my target!!! whats going on? :S

That depends, what all did you change? Is your target near/in goodsprings, and are they in an enemy faction? That would cause everyone to attack them.

i completely stripped factions out and started again! i made the target NPC a "wastelander" or something, even made that faction allies with GSfaction!

so basically i dont think its factions? the NPC is in the GSAbandonedshack cell, which isn't really in GS tbh....

Post some scripts/quests setups here boy, let's see what's going on. NPCs generally don't attack someone unless
1. They are hostile towards them and can detect them
2. They are being explicitly scripted to do so, i.e.

someNPC.addScriptPackage gotoThatCell
if someNPC.getincell ThatCell
someNPC.startcombat TheTarget
endif

Your case sounds pretty weird... Are you messing around with the Run Goodsprings Run quest?