From a user interaction POV, just have a couple of accounts. I started out on a small server, got a .world and kbin account, then got a beehaw account. If a server is down, I just switch instances.
From a community standpoint, it's terrible because the instance hosts the only live version of the communities. IMHO communities shouldn't be instance specific. Every (federated) instance should have a two-way aggregation of identically named communities. That has some (minor) drawbacks, but is much better for new users to understand and is much more resilient to individual instance failures and outages. (/rant.off)