Occasionally, I have conversations with people in the insurance industry and they believe that a $10 billion tornado (2010 dollars) is extremely unlikely to impossible.
This article from Insurance Journal bolsters my instinct on this.
As of July 15, insurance companies had already paid out $745,000,000 in Joplin. They expect claims to reach $2,000,000,000.
There is a rule of thumb that total losses are usually about 50% above insured losses, so that would take the total to $3 billion. That's right, insurance claims of three billion dollars in Joplin, MO, population 50,000.
Now, I will be the first to state the Joplin tornado was one of extraordinary strength and width (it wasn't notable in terms of path length). Once the Joplin tornado was east of the city limits, it hit very little. In other words, the tornado ran out of city. That would not be true with a similar tornado in Kansas City, St. Louis, Chicago, or Dallas-Ft. Worth.
Joplin is not densely populated as the cities just mentioned and the Joplin tornado missed the city's downtown.
If a tornado were to, say, move from Arlington (Texas Stadium - 6 Flags Area) to Downtown Dallas then across east Dallas, I believe the damage could easily top $10 billion.
I fear it is just a matter of time.