First question would be, how are you deleting them? Are you deleting via the Work Order and the same relationship used to display the assignments, or are you querying and deleting separately? And are you saving the delete transaction?
First option is to use the same relationship, via the Work Order, to delete the records, and then save the work order. This should automatically refetch the record and all relationships, showing the data is changed.
Next option would be to delete the way you currently are, but then force a refresh of the whole record, or just the relationship used to display the assignments.
Key point is, the view is only changed on fetching the data, or when you update the record or relationships being used in the display.