I have been digging and it seems:
1) There is no native/built-in failover solution for Drools Fusion 6
2) There is support for persistent sessions but it appears they are limited to save all/retrieve all, e.g. no ability to efficiently add and remove single events like hibernate would add/remove a single record from a DB. This would be expensive for a large, long running data set (STREAM mode)
3) Persistent sessions is a partial solution and I am unclear how we would even operate a cold/warm/hot standby
On the other hand Storm and Trident handle all aspects of failover but have limited support for CEP, I am debating using a custom solution with storm and storm tick tuples, but hate to reinvent the wheel.
I think in Storm Trident the state has to be relatively simple so it can fit into a key-value(s) pair, and the value cannot be too large. Such as a count or sum or some simple aggregation per key. Most people seem to use some time-based key and total up stuff with Trident. If there is complex state and multiple keys Storm Trident seems to falls down and cannot guarantee fully consistency between all states. Complex event processing keeps rich state such as intermediate pattern matches, derived indexes or data windows for many queries and many contexts. All that doesn't map well to Trident. Depending on your requirements Trident may be good enough.