The trick is, one person's impossible scenario is another person's normal operating condition.
I've made chat software work when DNS is broken. Other people say that's an impossible situation.
I've made chat software work when DNS is broken. Other people say that's an impossible situation.
But that also means you need to have IPs that will last for as long as your client lasts. Which means you need to have a defined lifetime for your client. And you need to have some mechanism to validate the IPs are still your servers and not been taken over by someone else (mutual authentication).
It sounds like implementing this scheme without a method to rotate IP addresses would be a mistake. But maybe I'm missing something.