Just to provide a bit more of an update. My husband is feeling generally better about the situation. He has spoken more with his PI and made arrangements that another post-doc in the lab will perform any required follow-ups after he leaves and that she'll be co-first author (with my husband still first in the list). He is preparing the manuscript and does hope that it will be submitted prior to his leaving the lab. He will also continue to correspond and assist in giving advice/writing even once he leaves. His PI's tone has been better and not as threatening. He is careful not to burn bridges and hopeful that the work will still be published and properly attributed.
As a point of clarity for those who wondered why he was so concerned, he feels the work he is publishing is very high impact and in a hot area of which contributes to his strong feelings around leaving even as he transitions to industry. I suppose most people feel this way about their research but he is particularly passionate.