Is there something to rescue from an Oracle Data Modeler design just with the 'logical' folder?
It could be possible to rescue the ERD - if the files in the "logical" folder are intact.

Perform the following steps:

Load the datamodeler, create a new model (name here: new_model), leave it empty, save it.

{1} Operating system/file manager: Give the new_model's "logical" folder a new name.
(Avoid name clashes with the rescued "logical" folder.)  

{2} Operating system/file manager: Copy the rescued logical folder into the new_model's folder.

{3} datamodeler: Close the new_model.

{4} datamodeler: Re-open the new_model.  Right-click Logical Model, click Show.

Example session (Linux)

# Directory listing _after_ the (empty) new_model has been created and saved.

[oracle@vbgeneric Documents]$ ls
new_model  new_model.dmd  erd_one_to_many erd_one_to_many.dmd

[oracle@vbgeneric Documents]$ cd new_model

[oracle@vbgeneric new_model]$ ls
businessinfo          datatypes        dl_settings.xml.merge_conflicts.local  mapping  rdbms
ChangeRequests.local  dl_settings.xml  logical                                pm

[oracle@vbgeneric new_model]$ mv logical renamed_logical

[oracle@vbgeneric new_model]$ ls
businessinfo          datatypes        dl_settings.xml.merge_conflicts.local  pm     renamed_logical
ChangeRequests.local  dl_settings.xml  mapping                                rdbms

[oracle@vbgeneric new_model]$ cd ../erd_one_to_many/

[oracle@vbgeneric erd_one_to_many]$ cp -R logical ../new_model

[oracle@vbgeneric erd_one_to_many]$ cd ../new_model

[oracle@vbgeneric new_model]$ ls
businessinfo          datatypes        dl_settings.xml.merge_conflicts.local  mapping  rdbms
ChangeRequests.local  dl_settings.xml  logical                                pm       renamed_logical

# Close the new_model.
# Re-open the new_model. Show Logical