I just saw a very recent film that had part of the same idea as "Last Salute For Commodore." A husband gets rid of a murder victim because all the clues point to his wife, but ends up getting arrested for the murder himself. And at the end, when they're both cleared of the murder by the police, the movie glosses over any other legal trouble for him, and shows him free.
Since he didn't murder anyone, I hate to think about it, but how much trouble would Charles be in for covering things up for Joanna?

He could be charged with tampering with the evidence of, and interfering with, a murder investigation. That’s certainly not as serious as losing your wife’s fortune.

The time frame of Charles Clay's death is not really spelled out very good. As a matter of fact it's not spelled out at all. And in the end, Sewanee only gets convicted of the Commodores murder. At least that's the way I see it. There was never a case or an investigation as to how clay died. And the audience is never subjected to any evidence as to how he was killed