Αν ο συνεργάτης μου αργήσει πάλι, η σύσκεψη θα αρχίσει χωρίς εκείνον.

Because this sentence is talking about a single possible future event: one specific case where the colleague may be late.

In Greek, that is usually expressed with:

• αν + aorist subjunctive

So:

• αν αργήσει = if he is late / if he ends up being late

By contrast:

• αν αργεί would more naturally suggest something ongoing, repeated, or habitual, depending on context.

So αργήσει is the normal choice here because the sentence is about this meeting, not a general pattern.

No. In this sentence, αργήσει does not mean past.

Greek uses the aorist stem in several non-past constructions, especially after:

• αν
• να
• θα

Here, the aorist shows aspect rather than past time. It presents the action as one whole event.

So:

• αν αργήσει = if he is late / if he arrives late
• not if he was late

The same thing happens in:

• θα αρχίσει = it will begin
• not it began

Because αν itself introduces the kind of verb form needed here.

Compare:

• να αργήσει = for him to be late / that he be late
• αν αργήσει = if he is late
• θα αρχίσει = it will begin

The verb form is closely related, but after αν you do not add να.

So:

• αν αργήσει is correct
• αν να αργήσει is not correct here

Θα αρχίσει is the normal way to form the future here:

• θα + verb form = future

So:

• η σύσκεψη θα αρχίσει = the meeting will begin

More specifically, Greek often uses θα + aorist-based form when talking about a single future action.

That fits this sentence perfectly: the meeting will begin once, as a complete event.

Because they are both in the same kind of form: a 3rd person singular aorist-based non-past form.

Their dictionary verbs are:

• αργώ = to be late
• αρχίζω = to begin

Their aorist forms are:

• άργησα
• άρχισα

From those, Greek forms:

• αργήσει
• αρχίσει

So the similarity is grammatical, not accidental.

Because Greek normally uses the definite article with possessives.

So Greek says:

• ο συνεργάτης μου = literally the colleague my
• η αδερφή μου = my sister
• το σπίτι μου = my house

This is completely normal Greek structure.

So even though English says just my colleague, Greek usually says the colleague of mine / my colleague with the article:

• ο συνεργάτης μου

Συνεργάτης can mean several related things depending on context, such as:

• colleague
• coworker
• associate
• sometimes partner/collaborator

In this sentence, because it is followed by η σύσκεψη (the meeting), the most natural sense is something like:

• colleague
• coworker

So the word is a bit broader than just one fixed English translation.

Πάλι here means again.

So it adds the idea that this is not the first time:

• αργήσει πάλι = is late again
• or more naturally in English, is late yet again

It often carries a slight feeling of annoyance, depending on tone and context.

That is a very natural position in Greek.

• αργήσει πάλι = is late again

Greek word order is fairly flexible, so you may also hear other arrangements, such as:

• αν πάλι αργήσει
• αν ο συνεργάτης μου πάλι αργήσει

But αργήσει πάλι is straightforward and idiomatic.

Changing the position usually changes emphasis, not the basic meaning.

Yes, χωρίς αυτόν would also be possible.

Here are the key points:

1. Χωρίς means without.
2. After χωρίς, Greek uses a strong pronoun, not a weak clitic pronoun.

So you can say:

• χωρίς αυτόν = without him
• χωρίς εκείνον = without him / without that one

You cannot say:

• χωρίς τον for without him

That is not how Greek works after a preposition.

As for the difference:

• αυτόν is the most neutral him
• εκείνον can sound a bit more emphatic, more detached, or slightly more formal, depending on context

So χωρίς εκείνον is perfectly natural, but χωρίς αυτόν would also be very common.

Because χωρίς requires the accusative case.

• εκείνος = nominative, used for the subject
• εκείνον = accusative, used after χωρίς

So:

• εκείνος αργεί = he is late
• χωρίς εκείνον = without him

This is a case change, just like Greek nouns change form depending on their role in the sentence.

Yes. Greek word order is more flexible than English word order.

This sentence could be rearranged in ways like:

• Η σύσκεψη θα αρχίσει χωρίς εκείνον, αν ο συνεργάτης μου αργήσει πάλι.
• Αν πάλι αργήσει ο συνεργάτης μου, η σύσκεψη θα αρχίσει χωρίς εκείνον.

The basic meaning stays the same, but the emphasis shifts.

The version you have is very natural because it starts with the condition:

• If my colleague is late again...

and then gives the result:

• the meeting will begin without him.

Because the sentence begins with a conditional clause:

• Αν ο συνεργάτης μου αργήσει πάλι, ...

and then continues with the main clause:

• η σύσκεψη θα αρχίσει χωρίς εκείνον.

This is similar to English punctuation:

• If my colleague is late again, the meeting will begin without him.

So the comma helps separate:

• the if-clause
• from the main clause

Sometimes Greek can omit subjects, because the verb ending often shows the person. But here the full nouns are useful and natural.

For example:

• Αν αργήσει πάλι, η σύσκεψη θα αρχίσει χωρίς εκείνον.

This would still be grammatical, but now who is late has to be understood from context.

Likewise, if the meeting were already obvious from context, Greek could sometimes omit it too. But in your sentence, keeping both noun phrases makes the meaning clear and complete.