Hi Udo,
The missing disk is not important, but the VM appears to be dead without it. So, in that sense, perhaps the missing disk is important.
root@denpm1:~# cat /etc/pve/qemu-server/105.conf
bootdisk: ide1
cores: 2
ide1: Backups:105/vm-105-disk-1.qcow2,format=qcow2,cache=writeback,size=54G...