Substack going down overnight would also be an extreme event. I’m rooting against that place too, but my point is just that the difference is relative, not absolute.
This can be addressed in at least some cases by contacting people to let them know. That’s one of the reasons I like to amass lists of where my pages have been linked – which isn’t a 100% cure-all, naturally, but that’s a scenario where it’s possible to have some agency at least.
The reason I’m pointing this out, just so you know, isn’t just about technicalities for technicalities’ sake. It’s because I’ve noticed a pattern of custom domain names being over-emphasized, and there are times when that can cross a line from inaccurate to negligent. That’s something I expect I might write more about some other time.
Update 1/6/26: @manuelmoreale I expanded on those thoughts here.