I like your 'water cooling Celerons' analogy.
It is hard to beat a stock, as supplied by the telco, router with a generic Android phone for maximum uptime. If one connection is wired and the other is wifi then the computer handles broadband difficulties with no problems.
If you are actually serious about 'single point of failure' then you just need to live with someone that is likely to not pay the bills for electricity or broadband. Being insufficiently creditworthy to have better than a pay as you go burner phone helps too as every byte costs $$$. Living in an area where any nice toys will get stolen/destroyed also 'helps' as a refurbished laptop running linux is then only practical option. Congested wifi 'helps' too, a basic wifi booster with ethernet out becomes truly useful for 'blazing speeds', particularly if wanting your backup network to come from the local cafe or some neighbour with an easily Googlable password.
Having a local server for development and version control means that you are good to go when it comes to useful work even if there is no connectivity going.
For entertainment a regular FM radio works fine. Two refurbished laptops and a USB stick for bulk transfer of current project stuff makes it fully possible to pull an all-nighter even if there is no electricity due to bills-not-being paid reasons. A nice add is a Chromebook, those things designed for nine year olds with a battery that lasts 10 hours with no difficulty does the job with better wifi than any normal laptop, no fans and no thermal runaway.
Even better, the whole kit can be put in a modest backpack and a bit of couch-surfing later one can be back in business.
It is much more satisfying to do more with less, I would probably hate myself if I had a basement full of servers and only whiled away the hours on social media rather than do 'work'.
This budget ethos is anti-pattern but why should it be? The carbon footprint of operating on low-power refurbished hardware is penguin friendly and cheap. If your apps are supposed to be compatible with regular consumer PCs then it doesn't really help to have a beast of a machine with 4K screen, 32Gb or RAM and some quad Xeon. Maybe a linux toolchain with no virtualisation is better for making one's code performant on target devices. Obviously an SSD helps.
The kids and the grandparents can read books together if the devices are down. They can also listen to the FM radio. What's not to like?
Thank goodness I don't do company IT. Yes it would consist of two refurbished laptops hidden under the floorboards, servicing 50-100 office workers without any difficulty.