It can take anywhere from a couple of weeks to a couple of months for them to heal and begin showing new growth along the fresh edges. That said, green goniopora is a completely different animal, literally, from the red one I cut in the video. They are very nearly impossible to keep, and cutting them is often the beginning of them receding. It's unlikely that there's anything realistic you could have done especially if it was a fresh cut as they heal much better in the water they were in when cut.
Exactly the outcome most reef systems would see. The green ones are tough.
