Nah, they weren't "all talk about legal action". They threatened with legal action a few times, but everyone threatens about legal action in high profile cases, it's nothing new, it's simply a strategy where they hope the opposing party will think twice before publishing anything, even perhaps holding things back. Damage control.
The case wasn't "swept under the carpet", it's the police saying they have investigated the matter but have nothing to prosecute on due to lack of evidence and reasonable doubt. Essentially what most have been saying for quite some time, that unless there's some actual evidence it's going to be a he said/she said and that's rarely enough to get someone convicted.
Not sure why people are so naive that they actually think his legal advisors are going to tell Ronaldo it's a good idea to start filing lawsuits just to keep this case alive in the media. For them it's pretty simple, Police aren't prosecuting because there's no evidence, hey we've been saying all along he's innocent and the Police agree, case closed. As i've already pointed out, the potential upside of winning a case against Der Spiegel is very small compared to the publicity involved and the downside of potentially losing such a case. The documents in question is just a small part of the case anyway, and it's a major newspaper, so unless his legal team have been documenting what the actual content is and Der Spiegel refuses to accept it, it's going to be extremely difficult to convince someone that they've actually done something wrong. Most will see it as Der Spiegel being well within their rights to believe the content to be true, given the rest of the documents they've been given via football leaks, and that it's just a small piece of a much larger case where the major story is the woman who'se accusing him of rape and not a document.