What is the ruling regarding the prayer of the congregants if the Imam forgot a pillar of the prayer and was not reminded until after he had finished it, and then the Imam repeated his prayer but did not instruct them to repeat theirs?

If a pillar (rukn) of the prayer is omitted and cannot be rectified, the rak'ah (unit of prayer) in which the deficiency occurred becomes invalid. The worshipper must then perform a replacement rak'ah and subsequently perform a prostration of forgetfulness (sujud ba'di). If this is not done until a long time passes or the ablution (wudu) is invalidated, the prayer becomes void and must be repeated. The preponderant opinion is that "a long time" is determined by common practice. Accordingly, if the congregants (ma'mumin) omit a pillar such as bowing (ruku'), they must repeat their prayer.