For a couple of reasons, @Conversational has not turned out to work very well in practice, so I've replaced it with a new mechanism which simply detects that a page was rendered inside a long-running conversation and blocks and redirects any actions originating from that rendered page if the conversation has ended. Clearly the question is "redirects to where?", and that is the bit I don't loive so much:
In pages.xml and pageflow definitions, you can now specify no-conversation-view-id to define where we should redirect to (a similar effect to ifNotBegunOutcome="....").
If anyone has better suggestions of where to define this, and a better name than "no-conversation-view-id", please speak up.
The good news is that a bunch of problems with @Conversational are now gone. Eg, try refreshing a page from an ended conversation.
This stuff is demoed in the DVDStore and booking demo.