Law effortlessly defeats Buggy!
Buggy's dumb luck strikes Law, his unwitting victim!
They realize after about 30 minutes neither side can win so they both make like a banana and split.
Okay both opponents meet far away from the ocean. We assume neither opponent has haki, otherwise they can both use any abilities shown thus far. The fight is one on one, Law has his sword. To help Buggy let's pretend there are no objects on the battlefield (trees, rocks, that kind of stuff).
So basically, it's a pre-time skip fight. Okay.
Buggy is used to his body parts fyling around, so he sure has an advatage here. On the other hand, he could be dumb enough to make use of his Muggy Ball, which can only result in blowing up himself ....
Law destroys Buggy. Buggy's body parts flying around wouldn't be problematic. But we've yet to see Buggy throw around his internal organs. Law just takes out his heart. If Buggy's lucky, Law will keep him around for comic relief. Everyone should have a dose every now and then.
buggy would have no trouble with law's slashing however that is meaningless. Law wouldn't need to do such a thing to begin with, he is physically powerful enough to make fodder out of buggy. Heck, hitting him with a sheathed sword would do the trick, he would quite literally shot shot him. Buggy is not worth a damn even against people significantly weaker than pre timeskip law.