I don't have experience with something like this, but I can do a mini lab with something like this, to test the steps below .
What would I do.
0. Do you have metadata backup for XCP-ng?
If YES
1.1. I would reinstall the server from scratch, before make a backup with Clonezilla with the boot disk of XCP-ng ;
1.2. I would reconnect iSCSI, without formatting it - reinitialize, only reconnecting (to not delete the data on it);
1.3. I would restore the metadata;
1.4. The result should be all the info about the VM that was on XPC-ng, and hopefully it also attaches the iSCSI disks.
If NO
2.2. I would reinstall the server from scratch, before make a backup with Clonezilla with the boot disk of XCP-ng;
2.2. I would reconnect iSCSI, without formatting it - reinitialize, only reconnecting (to not delete the data on it);
2.3. I would redone the VMs from scratch and start attaching the disks to identify which and to which VMs they were attached before;
2.4. The result should be functional VMs
In principle, if you have the disks intact, the data is there, you just have to restore the VMs (RAM, CPU, attached the correct disks, etc.)
This is the menu for XCP-ng metadata backup, Backup/New.
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