Overall, I still believe in god and the animal story. And I believe the author is trying to make people believe in God:
1. Fundamentally, the movie isn't based on a true story. So just like most novels, it is the author wants to tell us something based on his/others’ experiences/. At the end of the day, to proof there is no god, a fake story is not enough, he has to illustrate more scientific or serious proof
2. About "Thirsty", I now agreed with you, it seems the story did imply Thirsty is PI.. So tiger's name changed, so was PI's name. There are many details to be noticed:
2.1. Tiger's name is changed to Richard Parker by human who believed in no god.
2.2. Ignore the fact PI changed his own name, just think he was "Thirsty", that name was before he believe in Christian god, isn't that implying, after he believes in Christian god, he is not "thirsty" anymore?
3. Now let's think about this, thirsty, without religion belief in the other version of the story, shows the darkness side of human.
PI, previously thirsty, who believes in god, show the greatness to “thirsty”.
So what the author trying to say here? Isn't he saying a human, depending on whether he believes in god or not, will do different things on different journeys, have a different story ending?
The animal version of thirsty, at the end of the journey, will care no others, so he would not look back. (Not think thoroughly yet, my mind still trying to give some nice comments to the tiger.)
The human version of previous thirsty, PI, still expected and tried to make connection between god and “thirsty” human.
4. Now, I have a feeling this story is use PI as a gift from god, again, to tell people, who all have sins, to believe in god and understand god, and do good things:
4.1: “Why god send his son to sin and killed by evil people” PI said that made no sense. However, he now released it made sense, so PI did the same thing, PI was sent to stay with curcial creatures, and what he did was to save his life , and tried to teach them to believe in god.
4.2 : At the end of the day, tiger still be tiger, who has no belief, will turn away from god. In bible, god says, the person who do not believe, only look for proof, they won't believe in the furture either. as I said last night, people who look for proof won't see the proof,
God won't take care of these people either, their hearts are like stones. So tiger didn't look back his savior, even though PI eventually still believe he can gave belief to him.
4.3: the two insurance staff didn't believe the story in the beginning, but was inspired and believe the story, which is an indication of PI's success in his mission. And PI passed this to the writer, who doesn't exist in the book, and the writer carry on to pass god's story along. PI succesfully connect god with human and leave legacy to the next generations. This is what Jesus did, pass his legay to others, inspired and changed normal human, and connect them to god. This back the point 4.1, why god send him into this adventure, because he then he can carry on his mission and pass this legacy to other humans till generations.
5. Back to the author again, the author seems knew well about these major religons. I personally believe, if he can write this book, it is not necessary for him to write against religon beliefs in this way. A possiblity is he lives in a very multicultural country, Canada, with even multi official languages, then he got a very deep understanding what religions’ true meaning to human. So he doesn't want people use religons as a mean to rule the world or to fight. In the history, religion were used against their enemies before. Hitler used it to against Jews too. I can show you a documentery talking about that in my external hard disk drive.
PI, from the author point of view, is sent to human by God with this mission. He did that successfully.
So, that’s all my thoughts at this time. what do you think?