the human root of identity is the handle (memorable/recognizable), but the real identity root for the account is a DID. which is a pretty open/wild spec, so we mostly use did:plc ("placeholder"), which is a self-authenticating tricky tricky.
withing the protocol and applications, everything under the hood works via DID references, not handle references. a domain handle works by pointing at a DID, but does not control the actual DID ("DID document"). so any old users/followers/href will still be attached to the "old account". and it would be possible for the old account to recovery and set up a new handle.
but the superficial bits (anchor text), and human identity for new lookups, are attached to the handle, and could get pointed to a new DID, or just not resolve. that would be messy.