If Leblanc makes a reflection unit and makes it a copy of a card, then Temporal Break is cast on the copy, what happens to the copy?

The Reflection is banished and ceases to exist permanently — it does not come back.

The copy is still fundamentally a token (copy effects only copy traits, not token-ness — FAQ #11371), and Rule 186.1 says a token that enters any Non-Board zone besides the Chain ceases to exist immediately. Temporal Breach banishes it first, so by the time "its owner plays it to the same location" resolves, the token is gone and that instruction is ignored (Rule 359.3.e.6). This is the same result as FAQ #11668: Temporal Breach on any token is permanent removal. Note this is not a kill, so nothing that triggers on Deathknell/kill fires either.