This looks like it's fixed now.
Almost everything has been moved from the opennms-server package to the opennms-common package.
All of the config files are now either in /etc/opennms, or are marked as conffiles, so debian shouldn't remove them unless you purge (not just remove) the package.
When removing a package, debian only deletes files that it actually installed (any files created after package installation will not be deleted), so it should not remove any data directories either (but it will remove them if you purge the package).
It will remove the 'etc' and 'share' symlinks in /usr/share/opennms/, so you would actually have to look in /etc/opennms/ or /var/lib/opennms/ to find the files, but they should be there.
root@nms-dev-data:/# dpkg -r opennms-server opennms-common
(Reading database ... 20824 files and directories currently installed.)
Removing opennms-server ...
Stopping Open Network Management System: opennms.
Removing opennms-common ...
root@nms-dev-data:/# ls /etc/opennms/
actiond-configuration.xml http-datacollection-config.xml rrd-configuration.properties
AvailabilityReports.xsl imports-Servers.xml rtc-configuration.xml
c3p0.properties java.conf scriptd-configuration.xml
capsd-configuration.xml javamail-configuration.properties service-configuration.xml
categories.xml jcifs.properties setIfServiceKeysOnInsertTrigger.sql
chart-configuration.xml jmx-datacollection-config.xml setIfServiceKeysOnUpdateTrigger.sql
collectd-configuration.xml ksc-performance-reports.xml setIpInterfaceKeysOnInsertTrigger.sql
configured libraries.properties setIpInterfaceKeysOnUpdateTrigger.sql
create.sql linkd-configuration.xml setSnmpInterfaceKeysOnInsertTrigger.sql
database-schema.xml log4j-controller.properties setSnmpInterfaceKeysOnUpdateTrigger.sql
datacollection-config.xml log4j.properties site-status-views.xml
destinationPaths.xml magic-users.properties snmp-adhoc-graph.properties
dhcpd-configuration.xml map.disable snmp-config.xml
discovery-configuration.xml map.properties snmp-graph.properties
eventconf.xml model-importer.properties statsd-configuration.xml
eventd-configuration.xml monitoring-locations.xml surveillance-views.xml
events notifd-configuration.xml SVGAvailReport.xsl
events-archiver-configuration.xml notificationCommands.xml syslogd-configuration.xml
events.archiver.properties notifications.xml threshd-configuration.xml
examples nsclient-config.xml thresholds.xml
exclude-ueis.properties nsclient-datacollection-config.xml translator-configuration.xml
getManagedOutageForIntfInWindow.sql opennms-datasources.xml trapd-configuration.xml
getManagedOutageForNodeInWindow.sql opennms.properties users.xml
getManagedServiceCountForIntf.sql opennms-server.xml vacuumd-configuration.xml
getManagedServiceCountForNode.sql PDFAvailReport.xsl viewsdisplay.xml
getManagePercentAvailIntfWindow.sql poller-config.properties vulnscand-configuration.xml
getManagePercentAvailNodeWindow.sql poller-configuration.xml webui-colors.xml
getOutageTimeInWindow.sql poll-outages.xml xmlrpcd-configuration.xml
getPercentAvailabilityInWindow.sql response-adhoc-graph.properties xmpp-configuration.properties
groups.xml response-graph.properties
root@nms-dev-data:/# ls /usr/share/opennms/
lib
root@nms-dev-data:/# ls /var/lib/opennms/
rrd
root@nms-dev-data:/#
This looks like it's fixed now.
Almost everything has been moved from the opennms-server package to the opennms-common package.
All of the config files are now either in /etc/opennms, or are marked as conffiles, so debian shouldn't remove them unless you purge (not just remove) the package.
When removing a package, debian only deletes files that it actually installed (any files created after package installation will not be deleted), so it should not remove any data directories either (but it will remove them if you purge the package).
It will remove the 'etc' and 'share' symlinks in /usr/share/opennms/, so you would actually have to look in /etc/opennms/ or /var/lib/opennms/ to find the files, but they should be there.
root@nms-dev-data:/# dpkg -r opennms-server opennms-common
(Reading database ... 20824 files and directories currently installed.)
Removing opennms-server ...
Stopping Open Network Management System: opennms.
Removing opennms-common ...
root@nms-dev-data:/# ls /etc/opennms/
actiond-configuration.xml http-datacollection-config.xml rrd-configuration.properties
AvailabilityReports.xsl imports-Servers.xml rtc-configuration.xml
c3p0.properties java.conf scriptd-configuration.xml
capsd-configuration.xml javamail-configuration.properties service-configuration.xml
categories.xml jcifs.properties setIfServiceKeysOnInsertTrigger.sql
chart-configuration.xml jmx-datacollection-config.xml setIfServiceKeysOnUpdateTrigger.sql
collectd-configuration.xml ksc-performance-reports.xml setIpInterfaceKeysOnInsertTrigger.sql
configured libraries.properties setIpInterfaceKeysOnUpdateTrigger.sql
create.sql linkd-configuration.xml setSnmpInterfaceKeysOnInsertTrigger.sql
database-schema.xml log4j-controller.properties setSnmpInterfaceKeysOnUpdateTrigger.sql
datacollection-config.xml log4j.properties site-status-views.xml
destinationPaths.xml magic-users.properties snmp-adhoc-graph.properties
dhcpd-configuration.xml map.disable snmp-config.xml
discovery-configuration.xml map.properties snmp-graph.properties
eventconf.xml model-importer.properties statsd-configuration.xml
eventd-configuration.xml monitoring-locations.xml surveillance-views.xml
events notifd-configuration.xml SVGAvailReport.xsl
events-archiver-configuration.xml notificationCommands.xml syslogd-configuration.xml
events.archiver.properties notifications.xml threshd-configuration.xml
examples nsclient-config.xml thresholds.xml
exclude-ueis.properties nsclient-datacollection-config.xml translator-configuration.xml
getManagedOutageForIntfInWindow.sql opennms-datasources.xml trapd-configuration.xml
getManagedOutageForNodeInWindow.sql opennms.properties users.xml
getManagedServiceCountForIntf.sql opennms-server.xml vacuumd-configuration.xml
getManagedServiceCountForNode.sql PDFAvailReport.xsl viewsdisplay.xml
getManagePercentAvailIntfWindow.sql poller-config.properties vulnscand-configuration.xml
getManagePercentAvailNodeWindow.sql poller-configuration.xml webui-colors.xml
getOutageTimeInWindow.sql poll-outages.xml xmlrpcd-configuration.xml
getPercentAvailabilityInWindow.sql response-adhoc-graph.properties xmpp-configuration.properties
groups.xml response-graph.properties
root@nms-dev-data:/# ls /usr/share/opennms/
lib
root@nms-dev-data:/# ls /var/lib/opennms/
rrd
root@nms-dev-data:/#