First of all this is a body transplant.
Secondly I absolutely hate the negativity surrounding this procedure. How will this ever become a reality if we do not try?
Unfortunately as this is the first attempt at such a complicated operation there's so many things that can go wrong. The odds are against him.
Now I'm sure they'll be able to attach the head to the body and re-establish circulation but I do not think the spinal cord will be able to be reconnected. He may live for a few days with a new body but just like the mice he won't lost long unfortunately.
I hope this does further our understanding and I really hope this one attempt is not the first and last one.
If cloning was pursued this procedure would have a much higher chance of success as the body would not reject the head. Imagine being able to grow a replacement body parts. That's the sort of science we're missing due to overzealous ethics.
Maybe one day we'll step out from the dark ages.