Cant really offer anything of substance that other people have but as with yourself try to exhaust every possible solution in which the cat can survive happily. If there isn't an option, or the option is incredibly difficult then again, as with yourself make sure the method is as painless and comforting as possible.
It's an incredibly difficult decision that honestly seems nothing but horrific. Still, it's very telling of your personality to worry about the overall well-being of the cat should you not be around. Cats, despite being assholes, are actually pretty good at seeing their bonded humans emotions. Im sure your cat, if they could speak, would understand and be appreciative to have been with you.
If you're going to go yourself then once again, please do so painlessly. It's what you deserve for whatever suffering life forced you into. Take care, both you and your cat. <3
I completely agree with your first paragraphs take but Jesus man. 2 weeks of dehydration for an animal who cannot possibly understand what's occurring is just horrific. Not to mention that the entire time the cat will literally be begging you for sustenance. Starving your animals is nothing but animal abuse. Might as well just torture the cat at that point.