With the newest patch, there is a new way to bring dead Sims back to life, and features the return of Ambrosia.
To make Ambrosia, you will need to reach Level 10 - Gourmet Cooking (implying Level 10 in regular Cooking), and Level 7 of Gardening.
You will need an Angelfish, Death Flower, and Potion of Youth.
- You get a Death Flower by grafting a Pomegranate and Orchid. (Pomegranates are made by splicing Apple and Cherry trees, while Orchids appear after you finish the Space Rock Collection)
- You can get the Fountain of Youth from the Rewards Store for 1500 Satisfaction Points.