Is the 'Isha prayer valid after the congregant stands to make up a missed rak'ah, then returns to prostrate with the Imam who prostrated for forgetfulness after the taslim and delayed in it, then the congregant makes up his rak'ah and prostrates for forgetfulness on his own?

Scholars have differed regarding whether a latecomer (masbuq) should follow the imam in the prostration of forgetfulness (sujud al-sahw) if it occurs after the salam. The Hanafis and Hanbalis are of the opinion that he should follow, based on the generality of the Prophet's (peace be upon him) saying: "Indeed, the imam is appointed to be followed. So when he says 'Allahu Akbar,' then say 'Allahu Akbar,' and when he prostrates, then prostrate." Also, because the latecomer's making up (qada') of his missed rak'ahs occurs after the imam has completely finished his prayer, and the imam has not yet finished. In contrast, the Malikis and Shafi'is hold that he should not follow, but rather stand up to make up his missed rak'ahs first, and then perform the prostration of forgetfulness, because the اقتداء (following) ceases with the imam's salam, and the hadith "Indeed, the imam is appointed to be followed" is specific to following during the main part of the prayer.