I do not know if this is true, but I heard that in the first gulf war, less military personnel died in the line of duty for the whole conflict than military members in the US due to natural causes, and accidents.
That being said many have died in the present conflicts in Afghanistan and Iraq, relatively however (although the loss of any service member is tragic) it is a small amount than in previous wars, like Vietnam, WWII, Korea etc.
I think it would depend mostly on your individual role. You could serve your whole career and never see combat, or you could see it often. A helo would probably be more at risk than a tanker.
If you want a good stat, look up the gulf war bit, but I don't think any stat would be representative, as it would be mostly dependant on your role. Certainly as a Marine, you will undoubtedly have non flying jobs, and, for instance as a FAC you could be in a lot more danger than at 50k ft. I am a civilian, but this is what I have gathered.