You will not be asked to refund any of the money if you make a sudden miraculous recovery. And the case can not be reopened no matter how much worse your condition later becomes. Unlike workers compensation, future medical is not left open. After settlement or trial the defendant and his insurer will have no obligation to pay for your continuing medical expenses, so it's important that your settlement is adequate. The settlement in a normal personal injury case is not taxable.
Punitive damages are taxable.
Interest later earned on the settlement funds will be taxable.