...
In the event that, after all of the above, no banner has been selected for display, then Revive Adserver will check if there is zone chaining in place. If so, then Revive Adserver will go to the next zone in the chain, and start the process from Step 1 above, with the new zone.
Step 5: Default Banner
In the event that Revive Adserver has not selected any banner to display at the end of all zones that have been considered, then Revive Adserver will display the default banner, if configured.
Otherwise, no banner will be displayed (i.e. a blank impression).