I think you're jumping to the "risky" conclusion a bit prematurely.
> What if they die or go bankrupt and no one agrees on who owns ETH?
By "owner", do you mean the core developers who own the protocol repositories on github, or do you mean the client software teams who own the software repositories, or the individuals and exchanges who run the nodes and economic services, or the stakers producing blocks, or someone else?
If two reputable factions have a simultaneous claim to be the protocol stewards of the "real ETH", the ETH currency will fork and market forces will decide who the "true" owners are by valuing each side of the fork properly. We've already seen something similar to this with Ethereum vs Ethereum Classic, and with Bitcoin vs Bitcoin Cash.
So we don't need to trust any majority of users like you said, you get to personally choose what fork of the software you want to transact on, based on what version of the client software you personally see as legitimate, and download and run.
> So I know who has ETH based on what software I download and I download software based on who has ETH? And I know I'm in the right cycle of that form because I googled it and found an 'authority'? Risky.
Every cryptocurrency has a cycle of that form, even PoW cryptocurrencies. You could take "the chain with the most accumulated work", but that's not enough, because what you really need is the chain with the most accumulated work that also follows the protocol rules, with the protocol rules being based on which software you choose to download. You always need to trust someone to give you the software, unless you download the source code, personally audit every line of it to understand how it affects the behavior of the protocol's consensus, and compile it yourself.