It's brought up in a conversation in Realm 2. I'm paraphrasing, but Naya essentially says, "Thank God my mate bond with Kali means I've stopped aging." So it seems that because she's bonded with an immortal, she's also become immortal.dont know if it gets explained later in the game, but isnt there a bit of an issue with Naya being the only one in the bond not being vampire/part vampire? just lifespan wise?
Edit: I see you answered your own question later already. Ah well.