It has come to my attention that, at the very least in 5E, Naga's are effectively immortal. When slain, they simply return to full HP in a matter of days. However, I have not managed to find any confirmation that the same is true in 3.5
Hence my question: Are Naga as immortal in 3.5 as they are in 5e? And if yes, then how could they be permanently put down?