If Nessie really loves Jacob then she might even sucide. Or might go into deppesion like Bella did when Edward left. If the eqution really is {Renesmee + Jacob = Love for them }then she will NOT be able to live without him.
I don't think he will die because there is no reason for him to give up changing into a werewolf. The Only way he can age is by stopping changing and since Renesmee will live forever, he will choose to stay werewolf and not age with her.
I think Nessie will react like her mother but in a controlled way like her father. Sure, for the first few days she'd be awfully sad but she'll manage to move on but will still love Jake because she's part vamp, means things are permanent for her.
But I think Jake can live forever, all he has to do is not to stop phasing. he just has to keep on being a wolf, which is possible since he within vampire vicinity
