Does the prayer of the congregants become nullified if the prayer of the Imam is nullified during the prayer, or do they complete their prayer individually?

If the Imam's prayer becomes invalid due to a reason not hidden from the congregants, and they follow him in that, such as his intentional omission of a condition of prayer (like facing the Qibla or covering the 'Awrah) or a pillar of prayer (like the opening Takbir or Al-Fatiha), then the prayer of the congregants also becomes invalid. However, if his prayer becomes invalid due to an excuse, it is permissible for him to appoint one of them as a successor. If he does not appoint a successor, then the congregants may put forward one of them to complete the prayer with them, or they may pray individually, except in Friday prayer.