Under the statuate of limitations, if there is NO contact between a debtor and a lender for 6 years, then the debt becomes statuate barred.
The debt still stands, however the lender can no longer take you to court to get the money back. This severely limits their options, and effectively means that if you refuse to pay then there is nothing they can do to get their money back. They can still continue to call you or send you letters, but cannot take you to court and get a judge to order you to pay.
After 6 years, the debt also drops off your credit file.