For a novel I’m working on. I’m curious as to the average amount of life insurance coverage a Fortune-500 CEO might carry. Anyone have any ideas?
How much he/she carries on themselves for their families (probably none), or how much the corporation carries on him/her?
Why do you hope that? 
The latter.
This wiki on Corporate Owned Life Insurancehas an unsourced quote:
“According to one source, Hartford Life Insurance estimated that one-quarter of all Fortune 500 companies have COLI policies, which cover the lives of about 5 million employees.”
If that is true then the average amount doesn’t tell you much since at least 75% of the companies don’t carry any insurance on their CEOs.
Typical employee benefit plans offer every employee the option of coverage of 1, 2, or 3 times their annual salary. Often the company will pay all or part of the 1 times amount, the rest is taken as a paycheck deduction. But at large group term insurance rates, so quite cheap.
That would be for payout to the benificiary selected by the employee, and usually capped at something like $200,000 or less. The OP is asking about Key Man insurance that pays the company if the employee dies.