Hi Satya, did you end up finding a solution for this?
If I understand you correctly there is a Call microflow activity in the workflow and in this Call microflow and number of other workflow are started. The parent workflow can only continue when all the other workflows are completed.
Answer: It's important to note that the workflows that are started in the microflow are not realy sub workflows as they have no connection to the parent workflow. They run side by side without knowing about each other. THis has to be build and can be done the following way:
In the parent workflow add a Wait for notification right after the Call microflow. The last activity in the "sub" workflow is a Call microflow where it's checking if this is the last "sub" workflow that is completed. If that's the case, use the Notify Workflow activity (in you microflow) to signal the parent workflow to continue.