I think Dooku will be dead way before Mace. It's been set up that Dooku is for Anakin (or *maybe* Obi-Wan) to take out. You better believe Anakin takes their last fight personally, so logically it seems that he would be the one to do it. And it makes a great opening sequence to the movie. From what SLJ and others have said, it seems like Mace is fighting more than one opponent (also makes sense he would take out someone with him that way). Like I've said before, fighting Grevious and his guards would be a killer (pardon the pun) way for Mace to die. Much cooler than Dooku I think.