Yes, under certain conditions. A discharge (cancellation) releases your parents from all obligation to repay the Loan.

Your parents’ PLUS Loan can’t be canceled for these reasons: You didn’t complete your program of study at your school (unless you couldn’t complete the program for a valid reason—because the school closed, for example), you didn’t like the school or the program of study, or you didn’t obtain employment after completing the program of study.

For more information about loan discharge or repayment: If your parents have a Direct PLUS Loan, they should contact the Direct Loan Servicing Center at 1-800-848-0979, or go to www.dl.ed.gov. If they have a FFEL PLUS Loan, they should contact the lender or agency holding the loan.

(Source: studentaid.ed.gov)