I can’t speak for actual Western billionaires but I had the chance to speak to a few Arab billionaires (member of the ruling families) and a few Western multi-millionaires (as in hundreds of millions).
In terms of the western ones: They don’t have a fear for their money,they have enough hidden accounts and real estate around the world that they will never run dry… They fear for the same thing: Their lifes. Basically in two ways: Partly they fear that some random leftist or a terrorist group like the Italian Brigate Rose or the German RAF will simply shoot them in the head or kidnap them so they can make a point. (Which is quite strange as none of the people I spoke with was even out of elementary school when these groups operated - but they were really afraid of them,not of some common criminal)
The other thing is that they all were really really afraid of ending like the Romanovs - that there would be some kind of political turn and all of a sudden the “masses” stand in front of their estate with pitchforks and torches and hang them. (That’s literally a quote from one of them) Funny enough: None of them were afraid of the right wing - even though their families sometimes literally once lost almost everything to the fascists, etc.
Personally that explains a lot of the current state of the world. Money will always gravitate towards right wing politics as the right wing is always fixed on a strong leadership structure - which makes it easy to identify who you need to “befriend” or bribe if you want to keep your money. And people who have seen political turmoil in a role where they felt unable to control their own social standing anymore also have a tendency to gravitate towards these structures. Et voilà you have a armchairs psychologists explanation for Elmo. Well,if you add in a LOT of ketamine.
My current strategy might be a bit over the top,but it works.
I have two main entities that contain data worth backing up - the NAS and to a much smaller extend my Proxmox cluster (which is partly within my house,partly at Hetzner).
User PCs do not have any User data saved, they all work with network drives mapped to the NAS, only irrelevant amounts of data are stored on them that gets backed up via Free File Sync. For the Notebooks I use the same concept as we are using a WG VPN 99,9% of the time anyway,but some important folders get also synched via Free File Sync for offline use if no mobile connection is available.
For proper backups I have basically three classes of data that I maintain: Prio 1: The real real important stuff. Photos of once in a lifetime events, important documents, etc. Prio 2: The stuff you still don’t want to loose. All other photos, the scanned documents, home folders, VMs/LXX backups, configurations, etc. Prio3: Everything else,mostly data that could be downloaded again. Easily. Movies, etc.
Prio3 data is currently only living in the NAS and does get backed up once in a while on a external hard drive. It’s mainly backed up as I am lazy and in case the NAS craps out I don’t want to reload all the stuff…that would take months.
Prio2 data gets backed up fully: For the NAS data: It gets backed up to B2 with versioning according to my needs (usually 3d,2w,3m,1y,but that depends highly on the source). Additionally full external hard drive backups every few weeks. (I would kill to get my hands on a proper tape drive again,I had one back in the day,but it was used and old and died) Some data is also stored on Synology C2 atm,but I will replace that soon with another cloud provider, likely Hetzner.
For Proxmox: Basically the same, but I use TUXIS instead of B2 and Hetzner instead of Synology C2. Additionally I have a old PC with Proxmox backup server which turns on once a week and safes the whole cluster before turning off again. In the future this PC is planned to replace the External hard disk’s,but currently hard drive prices are insane.
For the P1 data: Same as above,but it’s definitely staying on a second cloud provider. Additionally I also create archive blue ray disk’s every few month. (Usually every 4). These go into the safe deposit box at my bank and additionally to a second storage location.
And of course I have detailed instructions about this in my will so even if both my wife and I die my kid can figure it out.