Certainly possible that reflects John's financial situation and thought process. I'm viewing it more from the perspective that black mailers can easily go back on their word and continue to extort their victims after they are paid their initial ask.
Im this case, John didn't actually do anything wrong other than understandably not volunteer the fact that he argued with and punched Hal arpund the time he died. He could easily have the awkward convo with the sheriff about what went down, and then take away the blackmailers power and avoid having to pause investigation constantly to deal with her. Also, if I remember correctly, the $ was withdrawn from the business account, which likely would be fraud and unlawful uses for those funds. Even though I know John would face some serious risk telling the truth, I think he is increasing his risk playing along. Maybe I'm underestimating him and the writing and he'll donate the $ to the town in an official capacity and is just humouring the blackmailer briefly to buy time.
Depending on how his company is structured and his position at it, he could be kicked out of his firm for misusing company funds.