When a Reflection token created by conquering a unit with Deceiver's reflexive ability is moved to base before the copy effect resolves, does the copy still succeed if only the token moves to base, versus if both the token and the target unit are moved to base?

Yes — the copy still works if only the Reflection token moves to base; it fails only if the target unit is no longer at that battlefield.

Deceiver's reflexive trigger targets "another unit there," and that's the only thing with a location restriction. The token itself is not a target of the trigger — it's the object being modified ("It becomes a copy of…"), and moving to Base isn't a zone change, so it's still the same game object the copy effect applies to wherever it sits. Mirror Image proves the point: it makes the token at your Base copy a unit that can be at a battlefield, so the copy never requires co-location.

If the target unit is what moves to Base, the instruction mistargets — no unit matching "another unit there" — so the token stays a 0 [M] Reflection (and still gets Temporary, since that instruction doesn't depend on the target). Rule 359.3.e.9; copy effects are just a layer application (479.1), and the token keeps its token nature regardless.