That doesn't sound like his idea. Posthaven says they plan to exist long-term, but they aren't doing it in a way that if they do fail, you don't lose your blog.

Exactly: All your eggs are still in posthaven's basket (and i'm sure they have all the best intentions in the world!).

Thanks for the pointer! Yes, that's the concept that i'm aiming for, except that the user would bring their own hosting for even more chance of longevity (i assume posthaven has a bus-factor of 1 or maybe 2).