I can't speak as to whether or not the manufacturer of the seat belt was liable.  You would need to go over all of the facts of the case with a personal injury attorney.  However, you may not be able to sue anyway due to something known as the "statute of limitations".

A statute of limitations is a law which places a time limit on pursuing a legal remedy in relation to wrongful conduct.  After the expiration of the statutory period, unless a legal exception applies, the injured person loses the right to file a lawsuit seeking money damages or other relief.  The time in which to file a wrongful death claim in Louisiana is 1 year from the date of the death.

However, although people often speak of "the statute of limitations", in fact there are many statutes which apply limitations periods to civil actions.  Sometimes it can be difficult to keep track of the various statutes and their exceptions.  Again, speaking with an attorney as to all of this is advisable; a consultation for this type of case is free.

In Louisiana, you only have one year from the date of the accident to file suit.  Unless there is some countervailing reason (contra non valentum -- such as fraud) as to why you couldn't file within the year, your case has prescribed and cannot be filed.