The witnesses don't come back. They already testified, and the jury already came to a unanimous decision of murder 1. They are only retrying the penalty phase, so all the testimony and evidence are already on record. They can't go through new testimony with the witnesses because a) it isn't necessary, b) new testimony would be different than what they already testified to, and c) the defense can't retry the guilt/innocence phase since that's already been decided.
They aren't retrying the whole case, only the penalty phase with the new jury. The new jury will be given whatever evidence the prosecution decides they should know to bring them up to speed on the facts of the case and told that Jodi was found guilty of murder 1 and guilty of the crime being especially cruel. The defense can only use mitigating factors as to why her life should be spared. Jodi can probably give her statement again, and maybe they can find some people to testify to plead to save her life as they couldn't before... that I don't know about. They may have to go with just Jodi's statement since that's what they did the first time around.
It won't take a long time since the case itself is not being retried - only the penalty phase is being retried, but the new jury has to be informed on the facts of the case that have already been determined. What is going to take a long time is finding 12 jurors plus alternates that haven't heard about this case and that are also death qualified.
Everyone else stays the same... same prosecutor, same defense counsel, same judge, same defendant, etc.
I'm curious to know whether or not JM can bring in all those ridiculous interviews that Jodi did after recently throwing everyone including the jury under the bus.