Good morning Fediverse.
It should be a trivial undertaking for someone who knows Mastodon client apps, to build one that stores all your data. If your server goes down, e.g. you used the domain name democracy-now.ve domain name to host it, then the user still has all the data.
Exporting all the data to a new instance could also be a feature ;) I think gotosocial and mitra currently already have import functionalities.