Hello Miguel,
I hope you're fine. From what I understand it's a matter of workflow modelization.
Indeed you can run another workflow after a task as a subprocess, and the same way you can send data to the subprocess when initializing it, you can also receive data when the subprocess has ended. So it's possible to map this data to some control variables (e. g. a boolean is_ongoing which would be set to true when we receive some data when the subprocess ends, or a map of booleans { subprocess_id => is_ongoing }).
So in your workflow diagram right after the subprocess call you may create some kind of loop, like we go to a timer running every 5mn or so, after the timer has run we check whether the subprocess has finished : if the subprocess has finished we go to the next task, otherwise we loop back to the timer.
There may be other ways to achieve this, but this is what comes to my mind at first glance.
Best regards,
Raphaël.