Let's say the catcher is being DH'ed for in the seven slot. In the fifth inning The DH goes to the mound as a relief pitcher. A sub enters the game in the starting pitcher's lineup slot to catch. The starting catcher is out of the game by the removal of the DH.  Since he started along with the DH in the seven slot can he re-enter later in the game in the seven slot? Or does removal of the DH eliminate him from returning?

Here's what actually occurred which I believe was an illegal substitution. The DH became the pitcher. The catcher is in the lineup in the seven slot being DH'ed for. The catcher was moved to the removed pitcher's slot in the lineup and continued to catch.