Responses
Maybe the body gets old and at some point Tama goes back beign just a spirt? Mushu mentioned about the owner's soul going to heaven instead of staying with her body, so maybe they can stay together as spirits, if he doesn't need to move on, he could be just a ghost.
OMG YOU'RE RIGHT, I HAVENT THOUGHT ABOUT IT THAT WAY.
Since she's a demon so she doesn't get old and he's just a human, she'll probably watch him die of old age.