If there is not a mapping to some sort of immutable handle, i imagine some sort of announcement in the timeline(example.com has changed their handle to example.

If there is not a mapping to some sort of immutable handle, i imagine some sort of announcement in the timeline(example.com has changed their handle to example.xyz) and a history in their profile (handle = example.com 2017 to 2020-01-01. example.xyz 2020-01-01 to now) would cover it