Learn Spanish (Latin America): El evento estaría repleto y terminaría en la madrugada. - The event was probably packed and ended in the early morning.

In Spanish, the conditional tense is used to express guesses, probability, or wonder about the past. So, while estaría often means "would be", in this context it acts as a shortcut for "was probably" or "must have been". The same goes for terminaría ("probably ended").

Could I just say probablemente estaba repleto instead?

Yes, absolutely! Saying probablemente estaba is perfectly correct and means the same thing. Using the conditional (estaría, terminaría) to express past probability is just a very natural, native-sounding alternative you will hear often.

Why do we use estar (estaría) instead of ser (sería) with repleto? Isn't being packed a defining characteristic of this event?

Even if an event is known for its huge crowd, adjectives that describe how full or empty something is (like lleno, vacío, or repleto) always take the verb estar, never ser, because they describe a physical state.

Is repleto exactly the same as lleno?

They are very similar, but repleto is stronger. While lleno just means "full", repleto means "packed", "stuffed", or "overflowing". It gives a much stronger visual of a completely crowded event.