@Vu, Tue Thank you for reaching out to Microsoft Q&A, apologize for any inconvenience caused on this.
I have checked with Notification hub engineering team on this and sharing the below.
Currently, we don't have any mechanism to send alerts when a Notification Hub Ip address got changed.
Moreover, this seems to be a feature request, I would suggest you raise a feature request using this feedback forum. Our engineering team will actively monitor these requests and will check the feasibility to implement and work on it accordingly,
Feel free to reach back to me if you have any further questions on this.