Are Leblanc's legend copies still token units? So if Temporal Breach is played on one of those copies, is it played back or it ceases to exist?

Yes — LeBlanc's Reflection copies stay token units no matter what they copy, so Temporal Breach removes one for good: it isn't played back.

Copying only swaps copyable traits (name, Might, rules text, and even a cost gets appended per 185.3.a.2) — it never changes the object's intrinsic category. "Token" is intrinsic, and a token can't lose its token nature by any means (Rule 185.1.a). So when Temporal Breach banishes it, it moves to a non-board zone and ceases to exist immediately (Rule 186.1). The "its owner plays it to the same location" instruction then has no object to act on and is simply ignored (Rule 359.3.e.6).

Same answer for a real unit card in that slot — that one does get replayed, because cards survive in banishment. The distinction is card vs token, not copy vs original.