Will the congregation be rewarded for their intention when they do not pray in the mosque because it is impermissible to pray behind the Imam, and no other mosque is available?

If it is established that prayer behind the mosque's imam is not valid and no other mosque is available, then it is permissible to pray in congregation anywhere to gain the reward of congregational prayer, even if it is not equivalent to the reward of congregational prayer in a mosque. Prayer behind an imam who commits an innovation (bid'ah) that is not disbelieving (mukaffirah) is valid, and it is better than praying alone. This is the view of the Hanafis and Shafi'is. As for the Malikis, they hold that prayer behind an innovator should be repeated within the time limit. The Hanbalis, on the other hand, believe that prayer should be repeated behind someone who openly declares his innovation or is intoxicated. However, if his innovation is disbelieving, prayer behind him is not valid.