Assuming eventual availability can be pretty handy -- one way deal with a dependency outage is to retry with an exponential backoff. If a dependency is unavailable now, and your system keeps retrying until it is, then you are assuming your dependency will become available again eventually.
Fair point - but of course your client is not making any progress, and so the unavailability ripples up. It's unlikely that there is user facing case where this is a useful way to work, though I can see it's use in loosely coupled connections between backends.
