While PHM gave an admirable effort, it was never going to be a winning one.
One thing is for sure, Nadal needs to be outplayed. No gifts can be expected.
I think when you are aggressive (and you have to be all the time), you need to hit more volleys, sometimes speculative ones from mid-court, to give him less time to recover position during the points.
You should also use sharp angles and shorter balls to get him out of his comfort zone.
You should attack his backhand and go to the net as often as possible. You will get passed a lot but it might wear him down.
And you should try to attack his serve.
I wonder how an old school serve & volleyer would do against him. Playing chip-and-charge etc.
All easier said than down. But I know one player who can do all things that PHM did today, plus a few more.