Yes they can. Whether they win is another question. You shuld contact a local attorney to outline the risks and rewards of your action or inaction.
As my colleague indicates - anyone can sue anyone else. The real question is can they sue and win.
Pursuant to the statute of frauds, a contract to convey an interest in land must be in writing to be enforceable. Oral contracts can be enforceable, but they are fact sensitive and also require a higher standard of proof.
My "gut" is that if they were aware of the issue before closing and went to closing without resolving the issue, they would have a very difficult time now arguing for a different outcome.
I am not a LA attorney, laws vary from state to state, therefore you should always consult a local attorney.
If this answer was helpful, please mark it as helpful or as a best answer. This answer is for general education purposes only. It neither creates an attorney-client relationship nor provides legal guidance or advice. The answer is based on the limited information provided and the answer might be different had additional information been provided. You should consult an attorney.
Anybody can sue for any reason. If the buy sell contract did not say the seller was selling to a reservation of the mineral rights then I don't see where they have a valid cause of action. A normal sale includes all the rights that go with the property which includes mineral rights. You should carefully review the buy sell agreement. Louisiana uses a standard agreement that is legally required for most residential sales.
The first page provides a check off for mineral rights at line 30. If there is not a percentage listed in that line, and it is not mentioned elsewhere on the form then you should not worry.
Every situation is different and you should consult your own attorney to go over all the particular facts in your case. The answer given is only intended to provide general guidance regarding rights and responsibilities.