First we have to clarify who was the Son of Man the NT writers wrote about..
The term, "Son of a Man, is used by Jesus 80 times as a way to refer to himself (32 times in Matthew; 14 times in Mark; 26 times in Luke; and 10 times in a different way from the Synoptic Gospels in John). In all these texts Jesus is the speaker; no one ever addresses him as Son of a Man. The identification with Jesus is, however, in most texts clear, and in some texts even explicit e.g., Mark 2:10-11 "But I want you to know that the Son of Man has authority on earth to forgive sins. So he said to the man, I tell you, get up, take your mat and go home.” and Mark; 8:31 "He then began to teach them that the Son of Man must suffer many things and be rejected by the elders, the chief priests and the teachers of the law, and that he must be killed and after three days rise again."
So for someone who believes the Bible, Jesus said three times that he will return. Whether that was truly said (with divine knowledge) or made up by him or the authors, is another story.
The Baha'is have other problems. One that I argue about with them is their belief that Jesus didn't come back to life physically. Now, for me, I'm not arguing if it happened or not... I'm arguing whether or not the gospel writers make the claim that it did happen. And I think they did.
The strongest one is where the writer has Jesus has one of the disciples touch him, and Jesus tells him that he has flesh and bone and is not a ghost. Plus, in Acts it says that Jesus showed himself to be alive by many proofs. Yet... Baha'is say "no." That the resurrection was symbolic. And that the physical body of Jesus died and only his spirit rose.
Another problem for them... is that they don't only have to make it so Jesus, himself, doesn't return, but they have to explain how Kalki from the beliefs of some of the Hindu sects and the Maitreya from some of the Buddhists sects, is also their prophet, Baha'u'llah. It's not that clear... And it takes some very creative interpreting to get their guy to be the fulfillment of those prophecies.
They, naturally, think the interpretations make perfect sense, and it is obvious that their prophet is the guy.
But I think it is obvious that they do what they have to do to the Bible, to the NT, to any Scriptures to make their prophet fulfill what he needs to fulfill to be the guy... the return of the promised one, not only of Christianity, but of any and all religions.
But, absolutely for sure, it is critical for Baha'is not to have Jesus returning. He has to be dead and gone and a thing of the past.