Do relections still exist if the main target dies using leblanc

Yes — the Reflection token keeps existing either way. LeBlanc's Deceiver copies the target's stats once, then the two objects are independent.

If the target dies (or is returned/gusted) in reaction while the reflexive trigger is still on the chain, the token still enters play as a ready 0 [M] domainless Reflection with Temporary; only the "becomes a copy" instruction is ignored, because instructions that can't be followed are skipped (FAQ #10346, Rule 359.3.e.6). So you get a 0 Might token, not nothing.

If the target dies after the copy already resolved, nothing happens to the Reflection at all — copy effects permanently replace the object's copyable traits in the trait-altering layer (Rule 477.1.b), and nothing links the copy back to the original, so there's no reversion when the original leaves the board. Note the Reflection is still a token, so any bounce/return effect that removes it from the board makes it cease to exist (Rule 183.1).