Consider this:
"My husband just tried to kill me, I just killed him in self defence." - lots of attention, investigations, talking to people with a chance that someone might say the MC or Aletta were seen at the house right before Dwayne's death. That's an inconsistency in Cherie's story, more investigations, more questioning and maybe some accusations. Its a lot of trouble.
Vs
"Hello, Revenue service? I'm currently planning on divorcing my husband and I really want to screw him over. He hasn't paid taxes in so many years. But I don't know where he is!" There's an investigation, its a tax case, not a murder case. They can't find Dwayne, but instead of a body, they just presume he's left the country for some tax haven with no extradition. This has an added bonus, because in this case, while Dwayne is missing, he's presumed alive until proven otherwise. In many countries, there's a legal aspect called "Presumption of death", basically, depending on the country, if someone is missing for a certain number of years (depending on the country, this could be between 7 to 20 years) and there is no definitive proof that they are still alive, you can legally declare them dead.
Whether or not it was intentional, Cherie bought herself, Aletta and MC a lot of time, because the police aren't looking for a dead man, they're looking for someone who has committed tax evasion and fled the country. Those are two entirely different types of investigation.