(debtors may discharge more than $450,000 in student loan obligations in bankruptcy because payment of even a small portion of student loan debt would impose undue hardship on debtors as defined by 11 U.S.C. §523(a)(8); $22,000 of medical expenses incurred post-petition and debtor couple ages 60 and 58; sufficient evidence present of debtors’ health problems that limited employment prospects).