What is the ruling on someone who makes a mistake in the Iqamah (such as forgetting "Hayya 'ala al-Salah, Hayya 'ala al-Falah"), and is he required to repeat it if the worshippers become aware of his mistake?

If someone omits any part of the Adhan or Iqamah out of forgetfulness, then if the time elapsed is short, they should say the omitted part and then continue. If a long time has passed, they should repeat the Adhan or Iqamah from the beginning. And if they repeat it, there is no blame upon them. So, if the Mu'adhin forgets "Prayer is better than sleep" in the Fajr Adhan, and remembers it soon after, he should say it. But if a long time has passed, it is dropped and he does not need to repeat the entire Adhan, because it is from the Sunnah. If the Mu'adhin persists in his error and the mosque's congregants do not alert him, the prayer is valid and there is no sin upon them, because the Iqamah is considered a Sunnah by many scholars, or a communal obligation (fard kifayah).