^^^ Well it appears that she did arrest them both...
Yeah, but only after she'd stood there and done nothing while they smashed or destroyed a lot of stuff. And only because, implicitly, they continued to smash stuff after
she'd said that the next smash would get them arrested, implying that she wouldn't have arrested them for the previous acts of second-degree criminal mischief. And there was no later indication that they were in any legal trouble for their acts.
I did enjoy the scene where Esposito and Ryan were freaking out Castle though, that made me laugh.
My favorite part was how Beckett and Meredith ultimately handled the whole thing a lot more maturely than the men (or Lanie) expected them to.