Mark discovering that he might have feelings for Beth and his unborn child was hardly convenient. It didn't fit with him being and staying dead.
He must banish all thoughts of them, albeit barely formed. The warnings given by Bayliss were very convincing, but Mark allowed himself brief thoughts of a very different kind of life for him than currently planned, even if he could no longer be Rufus Johnson. He was young and had that sense of his own immortality.
If he really wanted to return to see mother and baby, he was sure he would find a way.