Resolvido.
[Unit]
Description=virtualbox windows vm control service
After=vboxweb-service.service
Before=shutdown.target reboot.target halt.target
[Service]
Type=oneshot
ExecStart=/usr/bin/VBoxManage startvm windows -type vrdp
ExecStop=/usr/bin/VBoxManage controlvm windows savestate
RemainAfterExit=true
KillMode=none
[Install]
WantedBy=multi-user.target