Si el partido terminaba en empate, habría prórroga.

Terminaba is the imperfect indicative, and here it helps express a condition seen from a past point of view.

This sentence is the past-version equivalent of:

• Si el partido termina en empate, habrá prórroga.
  If the match ends in a draw, there will be extra time.

When that same idea is reported from the past, Spanish often shifts the tenses back:

• termina → terminaba
• habrá → habría

So terminaba does not necessarily mean the match actually ended in a draw. It means: if that happened, then...

By contrast:

• terminó = ended / a specific completed past event

That would sound more like you are talking about what actually happened, not about a condition.

Habría is the conditional tense of haber, and here it means there would be.

It is used because the sentence is describing something that was in the future relative to a past moment:

• first, the match might end in a draw
• after that, extra time would happen

So habría works as a kind of future-in-the-past.

Compare:

• Si el partido termina en empate, habrá prórroga.
  present/future viewpoint

• Si el partido terminaba en empate, habría prórroga.
  past viewpoint