Legal verdicts don't "offset" if both parties have debts, is my understanding.
They will both have to go thru separate collections.
However, Heard is finished. She will file bankruptcy I'm guessing once she buries what she can in personal assets. As such her collection actions are turned over to a 3rd party. Depp could settle that for 10 cents on the dollar.
My guess is Johnny lives thru a revokable trust, which is probably tight.
He will levy her Aquaman residuals and come out way ahead once interest is imputed.