Does the worshipper's rak'ah become void if he does not hear the imam's takbir to rise from prostration, and remains prostrating until the imam prostrates the second prostration?

The rak'ah is not invalidated if the worshiper lags behind the Imam due to an excuse. He must then follow the Imam and catch up on what he missed. If he does not do so, the rak'ah is void, and he must perform another rak'ah in its place after the Imam's taslim (salutation of peace). This is the well-known position among the Hanbalis and Shafi'is.