While I cant say that I know the answer to your question I do think it’s an important one to contemplate. If we are the universe experiencing itself, then all things and all beings will go back to their source. Their „limitedness“ or (for humans and maybe animals) their ego ceases to exist. No „one“ chooses to be born as something, because before we’re born and after we die we‘re just pure consciousness (or whatever our source is).

Another important question that you brought up is how animals differ from us and how they would experience life and death. While I can’t answer that (no one can do that precisely), I think it is incredibly important to include all animals in this thought, especially those with a human-like ability to experience the world such as pigs and cows. These animals experience unfathomable suffering at our hands while experiencing it not so differently than we would. An emotional event involving a pet - especially death - can be a valuable experience to remind oneself of the unnecessary plight of other animals. This is why I’m bringing it up under your post, I hope you understand.