Looks like there is much more broken than it looks on first sight.
I moved from pve to VmWare and installed vmware-tools into it. While installing the tools i noticed that there are a couple of Programs maked as “no longer needed”
Die folgenden Pakete wurden automatisch installiert und werden nicht mehr benötigt:
bc cgroupfs-mount containerd docker.io git git-man
golang-docker-credential-helpers heimdal-kdc heimdal-servers ifplugd
libapache2-mod-authnz-pam libapache2-mod-wsgi libdaemon0 liberror-perl
libfile-copy-recursive-perl libio-socket-inet6-perl libirs141
libkdc2-heimdal libmcrypt4 libsecret-1-0 libsecret-common
libsnmp-session-perl libsocket6-perl libxkbfile1 libyaml-0-2
linux-image-4.9.0-14-amd64 linux-image-4.9.0-14-amd64-signed mrtg
nfs-kernel-server openbsd-inetd pass php-curl php-krb5 php-ldap php-mcrypt
php-memcache php7.0-curl php7.0-ldap php7.0-mcrypt pigz python-alabaster
python-babel python-babel-localedata python-bs4 python-cherrypy3
python-click python-colorama python-decorator python-defusedxml
python-formencode python-genshi python-html5lib python-imagesize
python-jinja2 python-lxml python-mako python-markupsafe python-memcache
python-mimeparse python-paramiko python-paste python-pexpect python-psutil
python-ptyprocess python-reportlab python-reportlab-accel python-repoze.lru
python-repoze.who python-routes python-ruamel.ordereddict python-ruamel.yaml
python-sphinx python-tempita python-trml2pdf python-typing
python-univention-directory-manager-rest python-univention-directory-reports
python-uritemplate python-urllib3 python-webencodings python-webob
python-yaml python-zope.interface python3-cached-property python3-chardet
python3-defusedxml python3-dockerpty python3-dockerpycreds python3-docopt
python3-jsonschema python3-texttable python3-urllib3 python3-websocket
python3-yaml runc simplesamlphp sphinx-common stunnel4 tree
univention-apache univention-apache-vhost univention-bind
univention-directory-manager-rest univention-directory-notifier
univention-directory-reports univention-docker univention-firewall
univention-heimdal-kdc univention-ifplugd univention-ldap-acl-master
univention-ldap-config-master univention-license-import
univention-maintenance univention-maintenance-mode
univention-management-console-frontend univention-management-console-login
univention-management-console-module-ipchange
univention-management-console-module-join
univention-management-console-module-mrtg
univention-management-console-module-passwordchange
univention-management-console-module-quota
univention-management-console-module-reboot
univention-management-console-module-services
univention-management-console-module-setup
univention-management-console-module-sysinfo
univention-management-console-module-top
univention-management-console-module-ucr
univention-management-console-module-udm univention-nfs-server
univention-policy-tools univention-quota univention-role-common
univention-role-server-common univention-saml univention-saml-schema
univention-server-overview univention-system-info univention-system-setup
univention-web-js univention-web-style update-inetd x11-xkb-utils xclip
xmlsec1
Verwenden Sie »apt autoremove«, um sie zu entfernen.
As this is my Domain Master these Packages sound to me like they should not be uninstalled.
My Question now is: What needs to be reinstalled to bring back my UMC?
The Domain is now unconfigureable as the Domain-Backup-Server throws an Error when i try to configure anything from there. : 
Any help would be very appreciated.
Greetings
Matthias