Our current high availability support only handles when a node disappears for a while, then comes back unharmed. I.e. we have no method of syncing information that was lost.
A common scenario would be one node being completely destroyed (fire, file system corruption, etc.). The node would then be replaces by a fresh install of ThinLinc. The system should then be able to re-populate this fresh node with data from the surviving node.
As a bonus it would be nice to detect lost sessions as part of a crash and sync those as well (or trigger a complete resync).
A workaround would be to temporarily stop vsmserver on the surviving node and copying over /var/lib/vsm/sessions to the freshly installed node.
That will still risk some noise in the logs though as the surviving node will try to push changes that are already in the session database as it tries to get rid of its HA backlog.
We've actually documented this workaround in the TAG since 2005: