On possible way is to use if-else statement to check if field.DataValue == null or not and respond accordingly. But following code can be used to make fields not required, required and business recommended.
Hope this helps. Please drop some comments if script is helpful.
crmForm.SetFieldReqLevel("fieldname",0);// set field to not required
crmForm.SetFieldReqLevel("fieldname",1); // set field to required/mandatory
crmForm.SetFieldReqLevel("fieldname",2); // set field to business recommended
Note: The above code is not supported by Microsoft.
