From what I gather, early on there were two distinct (but related) conspiracy theories around this case.
The first one was that Cotten was spending or otherwise personally diverting the funds, and it wasn’t just a matter of not being able to get to the money due to a lack of access to his system, but that it wasn’t there,
The second was that he faked his death to avoid prosecution.
Sometimes conspiracies actually happen. A theory is more likely to be true depending on how few people need to be involved to keep the secret. Cotten had no employees, no partners, he was a one man show. It seems like at most his wife may have been complicit in what he was doing with the funds, but I don’t think even that has been shown or would be necessary. So the theory that there was no money in those wallets was highly plausible, and based on subsequent investigations it seems like it was in fact true.
On the other hand, faking his death in the manner alleged is implausible to the extent of being fantasy. It would be one thing if he vanished without a trace, leaving behind a suicide note or something. But in this case he died at a hospital, where a death certificate was issued, and presumably his body was sent back home for burial. Faking something like that requires so many people that it gets into crazy land. It should be safe to assume the man is in fact dead.