This was new to me

[harmbu]

The ROLE of the designated hitter is terminated for the remainder of the game when:
a. the defensive player, or any previous defensive player for whom the designated hitter batted, subsequently bats, pinch-hits or pinch-runs for the designated hitter

I know that he cannot re-enter as the DH, but as a starting player he can re-enter the game. He would simply be a pinch-hitter and not the DH.