what happens if oppoent reacts with rebuke to my reflection token unit

It depends on when they're playing it — Rebuke is [Action], not [Reaction], so they can't "react" with it to anything on the chain. They can only cast it during their own turn's Main Phase, or in a showdown when they have focus and the chain is empty (FAQs #3425, #5934). If you mean they cast it on their turn at a showdown while your Reflection token sits at a battlefield, that's legal.

When it resolves, the token is returned to its owner's hand and then immediately ceases to exist, since tokens can't exist outside the board (Rule 186.1). It is not killed — so no Deathknell and no "when I die" triggers fire, even if the token had copied a unit that has them (FAQs #122, #10316). The actual card it copied stays right where it was; nothing else changes.

Unlike Gust, Rebuke has no Might restriction, so it doesn't matter what your Reflection copied — it still gets bounced. The only way it dodges is if it's at your Base, since Rebuke requires a unit at a battlefield.