There is no one who is replaceable, at least that’s how I feel.
The things that people do can often be done by others, but we are more than just one or two things we do. Are you just your hair? Just your looks? Just the way you speak? The way you dress?
If “you” consists of only one or two things then, yes, you could be replaced, and others can be replaced. But, who or what we are is an amalgamation of many things that are intertwined.
Your past influences who you are. Your physical look dictates how people treat you and how you view yourself. You actions play a role in your past, present, and future. Your actions and words affect how people view you, the things they do for you and to you. Your thoughts, and unexpressed tie into all of these things as well.
Someone can stand where you stood. Do the job you did. Say the words you said. Someone can look similar to you. That person can be better in some regards, they can be worse in some regards, they can even be equal in some regards, but they will only replace a part of what you do; they will not replace you.
You are an immensely complicated being.