In single cache scenarios, waiting for some time after the cache has disappeared is akin to standard BGP session keepalive protocols. However, several vendors have implemented protocol enhancements to immediately drop BGP sessions that have failed, rather than wait for the Hold timer to expire. I see value in that, and perhaps it might make sense for an RPKI implementation to support the same where it is more important for the RPKI data to be as current as possible.
6810 A client MAY drop the data from a particular cache when it is fully in sync with one or more other caches. A client SHOULD delete the data from a cache when it has been unable to refresh from that cache for a configurable timer value. The default for that value is twice the polling period for that cache. If a client loses connectivity to a cache it is using, or otherwise decides to switch to a new cache, it SHOULD retain the data from the previous cache until it has a full set of data from one or more other caches. Note that this may already be true at the point of connection loss if the client has connections to more than one cache.