Will I get killed if I visit Western Sahara on holiday?

No. You will not likely get killed, but you should be careful. Western Sahara is a very undeveloped area and has a lot of poverty. Any safety precautions you would take in a similarly situated country, like Guatemala or Belarus, you should take in Western Sahara.

Also note that Moroccan security forces patrol much of Western Sahara, so you should keep your papers on you at all times to avoid problems if you are inspected.
You are more likely to be killed crossing the road to reach the airport you intend to fly from. Take any advice given (I assume, by a travel agent, or hotel) and don't be too flashy with cameras and money.