Christian points an interesting aspect of the current implementation of the reliability in WCF. We all agree that we need some kind of persistence.
I am thinking something like it is done in MSMQ. When you create a message you can decide to have it durable or not (default). Then, we could have something like the following:
<reliableSession enabled="true" durable="true" />
Durable or recoverable (as in the BCL) ?