Does the prayer of a follower who did not notice the Imam's forgetfulness and did not perform the prostration of forgetfulness with him become invalidated?

Your prayer was not invalidated by your omission of the prostration of forgetfulness (sujud al-ba'di) that was incumbent upon the Imam. You should have prostrated with him when he did. It is sunnah for you to perform this prostration even if a long time has passed.