Is it permissible for a solitary worshiper, who led people in prayer during his (own) prayer, to say the Taslim and then perform the prostration of forgetfulness (Sajdat al-Sahw) alone, without involving the latecomers who joined him subsequently?

Prostration of forgetfulness (Sujood Al-Sahw) is permissible both before and after the salaam, and there is no disagreement among scholars regarding its permissibility. Their difference lies only in what is Sunnah and more preferable. Whether the prostration is before or after the salaam is desirable. The congregant must follow his Imam in the prostration of forgetfulness, and his prayer is valid if he prostrates after the salaam.