Well, that doesn’t make me feel much better! 
Ironically, I’m copying your response to Notes for future reference in case I need it to restore my Notes. How is that for convoluted thinking? 
I’d consider moving my notes to Obsidian, but dealing with attachments, especially on mobile, is a pain.
Woooooof this thread hurt to read.
For all I have read about how you work with Notes and methodically export to Devonthink, I would say that you are very safe regarding Notes, as you can recover your knowledge from Devon (in case of an Apple Notes disaster) or an offline backup (in case of a physical disaster with your machine).
Regarding Reminders… well it depends on your aversion to risk. Cultured Code publishes this information on how you can backup your Things database and although it is in SQLite format (so it’s trickier to move to another todo app) it’s a unique file that you could backup to an external disk and recover in a new Things installation. Omnifocus even has periodic reminders to backup your tasks.
One could argue that a problem with iCloud Reminders is remote, and it is, yet here we are all in this thread.
I also moved to Reminders a few months ago just try it out, and this thread make me a bit nervous 
. I have been playing with the “reminders-cli” app to do some integration with Alfred and it might also be possible to backup (or at least) export reminders with some scripting. I do not know if it will export all details, but at least it’s something.
Do you have an iPhone or iPad? If so are Reminders synced to it?
If yes then you may be able to Restore your iPhone or iPad to a prior iCloud backup. If you do that then the Reminders should be as of that prior date/time.
One would need to know if the iPhone/iPad iCloud backup will back up Reminders. It might not anything already in iCloud. The claim is that it will back up “your most important data” but doesn’t specify what that is. If you back up the iPhone/iPad to a Mac then it backs up "all of the data ".
Exactly. It’s the opacity of the details about syncing and backing up via Apple’s systems that makes me nervous.
Years ago (probably about 4 years), I tried to help a client restore a colossally screwed up situation — I can’t recall if it was Apple Notes or Contacts or Reminders. She had an iPhone, iPad, and Mac. I tried what I thought was a logical sequence of taking all but one device offline, fixing the data, then bringing them back online one at a time to sync. It always looked like the fixed data worked, but then it would revert to the old, corrupted data from the last backup. Then I tried wiping the data from devices before taking them offline. Still no dice.
Finally a long call to Apple tech support got me through the correct sequence to prevent the old backup data from poisoning the sync, but it required tech support changing something on their end.
In short, I love iCloud sync when it works. But if it fails, you are at the utter mercy of Apple’s own backups and they don’t seem to be taking it seriously enough. What @kevindern experienced is not acceptable.
At least, not for critical data — which for me is my to-do system, since it is also a planning tool. I will stick with OmniFocus. I once had to restore a OF database, and I got immediate support and was up and running with minimal data loss.
It seems like they could, at minimum, allow people to export, all at once, a PDF that contains all of the their reminder lists with their individual entries. It’s not so useful for backup, but at least they could get at their data! You can do this on a Mac, but only list one at a time. Tedious. Same for notes — you can’t select more than one note and get a pdf that contains all of the info; it only contains the first note in the selection. Sigh.
Bmosbacker, I share your initial thoughts. I reloaded OF v.3 and will run them concurrently for awhile. OF v4 beta is too buggy for my taste.
I’ve just checked my iMazing backup of my phone and reminders are not backed up by that - however Notes are.
I had not thought to run them concurrently for a while; that is a good idea. How did you get your tasks from Reminders to OF? I have 304 tasks in Reminders and many of them have recurring dates (some daily, some weekly, monthly, etc.).
I did not have that many — so, I took the time to retype them in. 
Even if I had 304, I would still retype them. OF can import from Reminders but then it removes them. Also, you will still have to review each one to make sure the repeating aspect is correct.
I would just take a project at a time. Type each reminder one after another. Go back and add the repeating aspects. Do this over several days.
Eventually, I will have to decide which system to keep as it is a hassle working both concurrently. YMMV. Keep us posted on your progress.