Gunslinger's right. The US judicial system is based on the principle of stare decisis, or legal precedent, and the decision of the Supreme Court to not hear a case does not set any type of legal precedent whatsoever. Thus, by not taking the Lousiana Supreme Court case at this time, the US Supreme Court has basically given autonomy over gun lawsuits to the states. Therefore, while gun lawsuits cannot continue in Lousiana per ruling by the Lousiana State Supreme Court, the outstanding cases in California are free to continue until the highest court in that state rules otherwise. Even then, that is no guarantee that the issue of gun manufacturer lawsuits is over.
It should also be noted that US Supreme Court decisions are only binding on matters of FEDERAL LAW. State Supreme Courts have the ultimate authority and the final say on all issues related to state law, unless those laws conflict with Federal law. Thus, states can also have their own laws regarding firearms (provided that they don't conflict with Federal Law), and should the California State Legislature, or some other state legislature choose to pass new legislation permitting gun lawsuits, there's really nothing the US Supreme Court could do. This is due to the fact that there is no Federal law which protects the firearm industry from lawsuits.