Expendable is a term that comes close though not exact. It implies that the object can be abandoned after use.

It is often used to refer to objects of little significance as in:

The servant was expendable, master had to be saved.

It can imply that the servant is replaceable. This ^[1] list notes replaceable as a synonym of expendable.

Substitutable can be another word with similar implications.

Dispensable is a great one. "Don't think you're indispensable. We can replace you."

I feel like I'm missing something, but easily replaceable or just replaceable seems like the obvious answer. Certainly, people are frequently referred to as irreplaceable when they're not easily replaced.

The word I might use is fungible.

In addition to the other suggestions, such people are sometimes referred to as "cogs" as in

I'm just another cog in this machine!

Where "machine" refers to some large impersonal organization that views its human resources as interchangeable components and that are individually replaceable.

This is because cogs in real machines are easily replaced and individual cogs (or other similar parts) really have no special inherent qualities that make them better than any other cog in the bag of spare parts.

Cog would be my preferred word (and I voted it up) but I've also heard the word "drone" used for a generic worker with no unique features. Also "grunt" borrowed from US military slang.

I have often used the saying 'dime a dozen' to refer to things that are low in value and easily replaced.

I think, based on your example, the word I would recommend is commodity.

The classic definition as shown on dictionary.com doesn't really work. But it is one of those words whose definition is changing as we speak, like access used to be something you did-now it's something you have. The word commodity used to be directly related to grains, trading and futures. In this context it means "that which is so common and available as to be nearly disposable."

And I think you'll find that people will know exactly what you mean (especially when used in the context of employment) without having to explain.

Redundant might be useful. It doesn't have the exact meaning you're looking for, but when applied to a worker it carries the meaning that there are others in the organization that can (and are) doing the job. Usually it's applied to a position, rather than a person.

For a darker twist, try disposable.

A pawn! A peon! A grunt! A stooge! A tool! A commodity! Nameless! Faceless! Anonymous! Unappreciated! Irrelevant! Unnecessary! Undifferentiated!

But if you were writing a movie script and you wanted just the right sardonic bite you'd use replaceable.

Another alternative is 'pawn', as in chess.

(Fungible's my favourite so far though...)

In the technology field, the term " plug-compatible ^[1]" is occasionally heard.

That originally ^[2] referred to products that were made as cheaper replacements for IBM mainframe parts (or whole machines); the connotation is that you can unplug the original, plug in the replacement, and have everything carry on working just the same, the two parts being completely equivalent as far as any interacting component can tell.

The term has been borrowed to describe people, as hackers are wont to do, or rather, to disparagingly refer to to the idea widely held by project managers and other suit-wearing troublemakers that technical people are just jumped-up bricklayers, and any one of them is just as able to lay some particular course of bricks as any other.

I'm a big fan of fungible, as others have mentioned. However, it is a bit obscure.

Words like dispensible or expendible are really more synonyms with disposable, meaning one-time usage.

The word I like to use is an indirect word; commodity. It's indirect because it's literal meaning is related to unprocessed goods, or something that is a 'product' rather than a service. The inference being that something is easily replaced because there are tons more just like it that can be easily acquired, like a McDonald's hamburger, or a box of kleenex.

It's usage would be Go ahead and quit, I don't care. You're a commodity to me.