Successor
Part of speech: noun
Definition: A person or thing that immediately follows another in holding an office or title. The next heir in order or succession. A person who inherits a title or office The integer immediately following another
Example sentence: Hey, nothing grows to the sky. There will be a successor movement. Right now it's nascent.
Replacement
Part of speech: noun
Definition: A person or thing that takes the place of another; a substitute.
Example sentence: Knee replacement is serious stuff. And it actually could have made me worse.