What is the ruling regarding an Imam who omitted the second prostration in the first rak'ah of a four-unit prayer and rose to the subsequent rak'ah, and did not return after the congregants glorified him?

If the congregants are certain that a prostration (sujud) was missed, they should glorify Allah (say "Subhanallah") to the Imam. If he does not understand, they should speak to him. If he does not comply, they should perform the prostration themselves, otherwise, their prayer will be invalid. They should then follow him for the remainder of the prayer and inform him after the salutation (taslim) to perform another unit (rak'ah) in place of the one from which the prostration was missed. If he does not perform it, his prayer will be invalid.