Thanks for the suggestion, but it did not help.
I tried on both the rescue from the opensuse installation dvd (image) and from the virtual machine with that extra disk added. In both cases:
It can’t be mounted with both mount and btrfs restore due to the errors
btrfs scrub was not possible because it was not mounted
btrfs rescue zero-log, super-recover and chunk-recover failed for the same reason
btrfs check --repair also was not successful. 
Does it seems that I must give up? 
Or someone has any final and hopeful suggestion?