You can use Microsoft Flow.
1. Create a new field called DateField (Date Time)
2. You already have your NumberField
3. Create a Flow which triggers on change of DateField
4. Delay Until "DateField"
5. Update NumberField to Null
6. Create a workflow
7. On update of NumberField --> if NumberField == Null --> Update DateField to Next month
Let me know if you encounter any issues.