I think it's much more likely that the result will be an un-deniable public insistence on the right to sue the royal family. And if the Sauds can be sued for 9/11, the US can be sued for all the drone strikes and the like.
In reality, the judgements of United States' courts could actually be enforced against the Saudis, by seizing their assets abroad. Any judgement by a Saudi court against the United States government is likely to be entirely unenforceable.