They don't care about abandoning us.
Sadly I don't think my ex cares about abandoning me for another man or how much it has hurt me. In fact I think she has probably convinced herself that I abandon her with my withdrawal due to the emotional pain she had caused me and that was all the reason she needed to allow herself and/or actively seek an emotional attachment to another man. She always had an excuse or reason for all the things she did that hurt me, especially the ones that she knew on some level were wrong.
She will paint over the guilt and shame for what she did with the idealization stage and "love" for her new BF. She will bury it and hide from it in the new relationship ... .until it resurfaces and consumes her and everyone that is close to her. She seems to have a knack for destroying everything that is good in her life and I don't see that changing.
So to answer your question ... .I think the fear will be quickly buried in a new relationship.
My stbxh to a "T".
He has "fantasy" relationships in his mind. He "love bombs" and "friend bombs". Whomever it is has to be just his. If not, he feels abandoned. Working, having separate friends, doing things with others (even my own children) was a problem for him ... .and in the end for me via his behaviors.
He already showed his true colors to some of his new (suppliers and enablers) "friends", causing some to drop out.
I know he is on the hunt for a replacement and has likely already burned through one or two. In his state, he is so desperate to fill the emptiness of being alone, he will scare anyone with some sense off with his neediness, constant calls, texts, stalking, etc.