I think you're being overly dramatic. In practice I've seen complexity (which HA setups often introduce) causing downtimes far more often than a service being hosted only on a single instance.
No need for SREs. Just add 2 more Hetzner servers.
from the "Serverborse": i7-7700 with 64GB ram and 500G disk.
37.5 euros/month
This is ~8 vcpus + 64GB ram + 512G disk.
585 USD/month
It gets a lot worse if you include any non-negligible internet traffic. How many machines before for your company a team of SREs is worth it? I think it's actually dropped to 100.
Risk management is a normal part of business - every business does it. Typically the risk is not brought down all the way to zero, but to an acceptable level. The milk truck may crash and the grocery store will be out of milk that day - they don't send three trucks and use a quorum.
If you want to guarantee above-normal uptime, feel free, but it costs you. Google has servers failing every day just because they have so many, but you are not Google and you most likely won't experience a hardware failure for years. You should have a backup because data loss is permanent, but you might not need redundancy for your online systems. Depending on what your business does.
"Run a script to deploy new node and load last backup" can be enough, but then you have to plan on what to tell customers when last few hours of their data is gone