I don't think people outside of the US understand how other countries deal with copyright issues. Most countries don't care and don't have laws to combat copyright infringements. No question MS has the ability to sue if the leaker is in the US but say the leaker is from a country like Lebanon (supposedly the location of the leaker) you honestly think MS has any clout? I can just imagine their legal team calling Lebaneses authorities and trying to pursue legal action on some guy who posted a video of a game online. They'll be laughed at and told to get lost.
The NDA isn't going to deter future leakers. If they had kept the beta within the US it would have been a different story. It's going to be a cat and mouse game for MS, they'll need to surf reddit and YT for any further leaks.