Hi Isaac,
There's not really a way to do this. The 'Run' call doesn't wait for the workflow to complete. The "Success" just means the 'Run' call was successfully sent to Automate, but the workflow could run at fail and you would still get the "Success" response.
This could be possible but would take a few extra steps. You could use the /workflows/{WorkflowID}/run call to start the workflow. A task in the workflow could make a /workflows/{id}/update call to update a workflow variable with the value you want returned. You would need to wait for the workflow to finish though, but you could then do a /workflows/{id}/get call to get that value.
