In the Redial conclusion to Future Diary, we see the 3rd iteration of Yuno living a normal life in the 3rd reality after the incident caused by the original Yuno and the 2nd Yuki saved her family's future. She has no recollection of Yuki at all in this world, even though she knows she is missing some very important memories.
This is almost identical to the state Yuki is in while trapped in the "ideal" world created for him by the original Yuno. However, she purposely removed herself from that false world, so it makes sense that Yuki can't even recall her name.
So what happened to the third iteration of Yuki that meant the 3rd Yuno couldn't remember him? He isn't seen at all in the final episode, so I'm confused as to what occurred in that regard. 1st Yuno wouldn't have had a reason to kill him as she wished to "try again" in that timeline, and Yuki, of course, wouldn't want to kill his own self.
Is there an explanation as to what happened to the 3rd timeline's Yuki?
And if he did still exist in that iteration, why can't the corresponding Yuno remember his identity at all?