Is it possible to delete a draft inside workspace once it has been saved? My only options are to complete, save in draft folder or to take this form offline.
If you mean you want to delete your incremental changes and reset the task back to its original state, then no, this is not permitted but there has been an enhancement request for it already.
If you want to delete the task completely, then no, not directly. You can only perform the actions that are defined in the process map for the step associated with this task. If deletion makes sense at this step, then you could add a Delete action that the user could choose to end the task and do whatever makes sense in the process map.