Over the years hundreds of people die in the Scottish Hills and Mountains. These are mainly winter climbing accidents or folk getting caught in exposed places with terrible weather and maybe inadequate gear. Although, I believe it is about 40 years since anyone died in a hill race there are a whole load of dangers reasonably close when you are running in the hills. Most of these are reasonably forseeable and include falls, exposure in poor weather, heat exhaustion, getting lost and spending longer out than is appropriate in light gear, lack of fitness, thirst and for the unfit heart attacks.
Organisers of races will generally only be in a position to know that you are missing (over a cliff or whatever) after the last runner is home. This means that you should have enough maps, compasses and skill to tell where you are going or start off by doing short races in good visibility. If you are lost or lying with a broken leg you should have enough to keep you warm for the several hours that it takes to mount a rescue after everyone is sure that you are missing. Generally the missing person is in the car park having been missed in confusion at the finish (rarely) or just having forgotten to report back. So the search won't get underway until an hour or two after the last runner has finished. You might in the worst case of a long race that finishes late be out overnight.
Make sure that you therefore take precautions to prevent this. Run in pairs where you are not confident about finding your way. Alaways ensure that you report to the finish if you retire, make sure that you are fit enough to run the distances you want, carry food, body cover and a whistle. If the weather is poor on the race day consider doing another on next week if you don't want to carry the necessary gear.
Finally remember that you need to keep the safety in perspective. I know of more people who have died driving to and from races than during them. Take care but don't let fear prevent you doing some decent races.