CacheDB and TTL

[Bruno Blanes via Unbound-users]

Hello again,
Why is it that CacheDB returns TTL 0 for items that originate from the external 
cache? Why not use the redis timeout when setting redis-expire-records?
Also, is it possible to make Unbound not stop in case the cache goes off-line? 
Could it fall back to resolving queries by default and periodically ping the db 
to see if it's back online?