If you copy the config to another node you can start it from the GUI on this node. Eg.
1) Node1 is down so login to node2
2) mv /etc/pve/nodes/node1/qemu-server/vm1.conf /etc/pve/nodes/node2/qemu-server/vm1.conf
3) Start vm1 in the GUI where vm1 will appear stopped on node2
Thank you @mir. I know that, yet there is no way for a not-so-experienced Proxmox VE user/admin to do that without going to command line. Therefore, a offline migration to another node is the only way to achieve this without going down to command line. And IIRC, you asked about a use case of offline migration: Could anybody give a good reason for migrating stopped VM/CT's?