Does The Mandalorian needs a new partner? Does we need The Child?

That's because people outside the show KNOW his real name. Palpatine wasn't named until The Phantom Menace, but it was still ok to call him "Emperor Palpatine" instead of just "The Emperor" before that movie came out.

It's never ok to call him "Sheev" though. His first name is Frank. That IS in the movie.