În cazul în care prelungirea nu este posibilă, restituim exemplarul.

În cazul în care is a more formal way to say if or in the event that.

Literally, it breaks down like this:

• în = in
• cazul = the case
• în care = in which

So the whole expression is literally in the case in which.

Compared with dacă:

• dacă = the normal, everyday word for if
• în cazul în care = more official, administrative, or formal

So this sentence sounds like something from a library notice, regulation, or formal message.

Prelungirea means the extension / the renewal, while prelungire means extension / renewal in a more general sense.

Romanian often uses the definite article where English might use a bare noun. Here, prelungirea refers to a specific renewal process already understood from the context, so the definite form sounds natural.

Also notice that Romanian usually attaches the definite article to the end of the noun:

• prelungire = extension, renewal
• prelungirea = the extension, the renewal

Because posibilă has to agree with prelungirea.

• prelungirea is feminine singular
• so the adjective must also be feminine singular: posibilă

Compare:

• prelungirea este posibilă = the renewal is possible
• transferul este posibil = the transfer is possible

So the ending changes to match the noun.

Both are correct.

• nu este is more formal and fuller
• nu e is shorter and more conversational

In official or written Romanian, especially in notices or administrative language, nu este is often preferred.

So:

• prelungirea nu este posibilă sounds formal and standard
• prelungirea nu e posibilă sounds a little more natural in everyday speech

The comma separates the introductory subordinate clause from the main clause.

Structure:

• În cazul în care prelungirea nu este posibilă = subordinate clause
• restituim exemplarul = main clause

Romanian normally uses a comma here when a clause like this comes first. It works similarly to English sentences like:

• If renewal is not possible, ...
• In the event that renewal is not possible, ...

Restituim is:

• present tense
• 1st person plural
• from the verb a restitui

So it literally means we return.

This form can be used in Romanian for:

• an actual present action
• a general rule or procedure
• institutional language

In a sentence like this, it usually means something like this is what we do or this is the procedure.

In Romanian, just like in English, institutions often use we in formal notices.

So restituim probably refers to:

• the library staff
• the institution
• the service provider

It does not necessarily mean a specific group standing there at that moment. It is more like an institutional we.

This is common in official Romanian:

• vă informăm = we inform you
• vă rugăm = we ask you / please
• restituim = we return

Exemplarul comes from exemplar, and here it means the copy or the item.

In library or document-related contexts, exemplar often refers to:

• a copy of a book
• a physical item
• a volume

So exemplarul is:

• singular
• definite
• the copy / the item

Important: although it looks a bit like English example, it does not mean example here. In this kind of context, it means a physical copy.

For the same basic reason as prelungirea: Romanian is referring to a specific, known item.

• exemplar = a copy / an item
• exemplarul = the copy / the item

In context, this would be the particular book or object being discussed. Romanian often makes this kind of noun definite when the reference is clear from the situation.

Here it is followed by the indicative:

• prelungirea nu este posibilă

That is normal. În cazul în care functions as a conditional connector meaning if / in the event that, and it does not automatically require the subjunctive.

So the verb after it is often just in the tense that makes sense for the meaning:

• În cazul în care vine ... = if he comes ...
• În cazul în care a sosit ... = if he has arrived ...
• În cazul în care va fi necesar ... = if it is necessary / if it will be necessary ...

Yes. A less formal version would be:

• Dacă prelungirea nu este posibilă, restituim exemplarul.

A more everyday-sounding version might be:

• Dacă nu se poate prelungi, restituim exemplarul.

The original sentence sounds more bureaucratic or administrative because it uses:

• în cazul în care instead of dacă
• the noun prelungirea instead of a more verbal structure like se poate prelungi

So the original is correct, but definitely formal in tone.