Rolling Back a Partial Upgrade
As long as you have not committed your upgrade to MarkLogic 9 or later, you can reinstall the earlier version of the server (MarkLogic 8.0-6) on each node.
In the event that you need to roll back an upgrade that has not been completed and committed, you can roll back the partial upgrade by re-installing the previous version of MarkLogic (for example 8.0-6) on the machines that have been upgraded.