its not a theory but it was mentionned in the game (lil reminder that theres 2 endings). althought,Idk how to answer the 2 last parts. idk if the cat is supposed to be ryuk from death note and if theres a specific reason on why zilas just didnt randomly die. but if i had to give u an answer, ig its prob how the cats "business" works. the death of someone is probably supposed to happen because of something (like the hate zilas got which lead him to suicide according to one of the endings).
Guys the reason on why you randomly stab Zilas is cuz it was supposed to happened.He actually died in the blizzard and sold his soul to the a kind of devil (one of the reason why theres was a random cat on his lap). But according to the deal, he had only a week to live, which explains why he wanted to get 1m, show "you" to everyone and propose to you. He also gave his soul because he realized that he did not care about the fame or many, but cared about wanting to spend time with "you", as his partner. It's one of the reason on why he said "Its not your fault...I can explain" + thats why you get no happy endings. Because of the deal, he knew he was about to die soon weither he liked it or not.
