Comment 7 for bug 1387978

IMO, as the volume is created by heat, if the volume deleted failed, it is reasonable for heat to delete failed.

But, I think there might be something can be done to improve for your case, for example.
when the volume deletion failed, heat will jump the deleltion and continue to delete other resources. Of course, the stack deletion result is failed with the infomation why stack deletion failed. Customer can manually delete the volume and then delete the stack.