Vampires cannot age so dying of old age is impossible. As is dying of a disease or intense injury as they are nearly indestructible.
The only way a vampire can die is from being torn apart by another vampire, because vampire venom is the only thing which can harm another vampire, and then setting the torn apart vampire alight, as the venom is very flamable. If the vampire doesn't get burnt, they'll put themselves back together.
Werewolves and Shapeshifters however are also capable of tearing a vampire apart.
Hope this helps :]