You can’t just cash them out and put them in your personal account. You have to use the funds to pay off debt, roll the funds into a new campaign, donate them to another campaign or donate them to charity. Even at the local level (city council) I had to do this.
Granted, you can use the funds to pay off debt to your own company or something (which your company would have written off or forgiven had you not had the funds to pay it), but even that all has to be declared in your campaign finance report. I’m sure there’s skeevy ways of using the excess money, but the money doesn’t simply become the candidate’s.