One of the hardest parts about losing a pet is after years of companionship is that you also lose that link to your past--the person you were when you first got the animal. And it reminds you of your own mortality, or at least reminds you that a significant part of your past is now gone.
I've had two pet cats die--Gretel and Henri. Gretel was my connection to Florida State and college, so when she died, I was like, Okay, now I've lived an entire animal's life since college. Henri belonged to my days as a twenty-something in Chicago. When he died, I could no longer pretend that my days of shopping for $2 skirts at the Brown Elephant were just around the corner. When I lose Ernesto and Emma Carol, I suppose I will be nostalgic for my first few years in Philadelphia. .
In any case, I'll miss Shiva. She was a good girl.