No skateboarder is in Tiger Woods territory in regards to importance to Nike, he is arguably their most important athlete outside of Jordan and Lebron. If Nyjah rumors like this become widespread they will do one of two things. First, is they just buy him out, pay the rest of his contract but stop promoting him in any way. The second, is they fire him with cause due to some offsetting morality language in their contract. Nyjah makes big money compared to skaters, but his deal is chump change for Nike, whereas Tiger they had a significant invested in. He also wasn't accused of anything illegal, just stuff that was immoral.
As for people talking about libel and slander. The onus, in that case, is always on the plaintiff to prove it didn't happen. Do you really think Nyjah wants to bring more attention to his lifestyle and antics? I'm sure he would just love the amount of written affidavits about the debauchery and drugs at his party. In this case, it's better just to let shit simmer more low key than bringing out all the other shit in open court. This is the main reason tear sheet gossip pages rarely get sued.