That's not exactly what nomadic identity is about, although it can also help with that.
The way nomadic identity is implemented in Hubzilla for example is that you can have accounts on multiple servers and by importing a shared cryptographic identity into all of them, other servers know to treat them as a single entity. Once that is established you can log into your account on any of the linked servers and use it normally. But if a server goes down or you decide to delete your account on one, you can seamlessly continue to use everything from another linked server.