Ran across an article by one 'Lyle Fitzgerald' noting the causes of death over his 4 year campaign. It contains a fair degree of accuracy, because of the over 600 deaths that it logs.
Now that's a number to reach for. That's a death every 2.4 days. I've been playing in old school campaigns for just over a year and only have 17 to my credit. Sadly, I have not been counting henchmen, which Mr. Fitzgerald seems to do, so my total is a little higher than 17 using his accounting system. Someday if I ever hit 100, I will certainly provide a similar statistical analysis. Here is his list of deaths.
"Goblin races (61) 10.1%
Dragons (45) 7.5%
Giants (34) 5.7%
General Combat (26) 4.3%
Lycanthropes (24) 4.0%
Execution/ torture, sacrifice (23) 3.8%
Undead (21) 3.5%
Bandits/ pirates/etc. (20) 3.3%
Giant insects (20) 3.3%
Assasination/ treachery (18) 3.0%
Giant rocs (18) 3.0%
Fireballs/ lightning (17) 2.8%
Trolls (16) 2.7%
Turned to stone (14) 2.3%
Guards, military patrols (13) 2.2%
Evil high priests (13) 2.2%
Man-eating vegetation (13) 2.2%
Related dragon species (13) 2.2%
Cursed items/ booby traps (12) 2.0%
Giant animals (12) 2.0%
Falls (12) 2.0%
Gnolls (11) 1.8%
Gargoyles (9) 1.4%
Hell Hounds (8) 1.3%
Demons (8) 1.3%
Elementals (8) 1.3%
Griffins (8) 1.3%
Kindred races (elves/dwarves)(6) 1.0%
Misc. spells (6) 1.O%
War (6) 1.0%
Misc. causes (85) 14.6%"
He notes that nearly 1 in 4 deaths results from the hand of man. He also notes 4 main factors that cause deaths from encounters are the power of the creature, the number of creatures, the willingness of the creature to attack, and the frequency of encounter. The main thing notable here is that the player approach has the most to do with the willingness of the creature to attack. In the end, I've found, players are most responsible for their deaths.
He also notes that the worst thing that can happen is to become surprised, even by relatively weak creatures. With this I agree. If you read my session logs, you can see that I might have killed 3 or 4 players earlier if their rolls hadn't been good when they were surprised by the Wyvern.