You can set a checkpoint beforehand by having an activity right after the metadata saving step to "retrieve field values", and get those two fields.  Then you can set a conditional sequence to check if either of those two fields are empty, and if so have it contain an email activity to alert the initiator if there is some way to insert an initiator variable into your workflow.  For instance, if it was a form submission, you could grab the initiator variable from there and put it in an email, etc.

I would prefer having the pop-up to appear right when the metadata is saved rather than to generate an email notification. I do have one workflow that is defined as a Business Process and Metadata Requirements specifies which fields should not be empty. When I trigger that business process, it does display a warning message if any of those required fields are missing entry.  Then my next question would be how do you convert an existing workflow into a business process?