Just to add, most underwriters won't insure a Stay at Home parent for more than $500K. We were told that that is the maximum, unless you can prove extenuating circumstances (like disabled children). This is how we are hoping to boost my life insurance, by citing the fact that both our kids have autism, that they were too young to be diagnosed with at the time we got our first policy.
A 10% return on investment IS pretty aggressive. I always thought the number to use for investments in terms of almost guaranteeing returns is somewhere between 4-8%. The stock market, over time, has averaged a return of almost exactly 7%. Of course, you can diversify and all that, but I think most financial advisers use that as a ballpark in order to estimate future earnings.
In addition, if you were investing a life insurance payout that you needed to rely on for long term income, you would likely invest in much safer, lower risk avenues, which would get you returns more around 4% over the long term. It would be foolish to put that kind of money in even a moderate risk investment category.