After 7 years of not paying a debt the debt can no longer legally be pursued and you cannot be sued for the debt after 7 years.
If the debt collector or debtor you owe the debt too has not collected the debt within 7 years or after 7 years and they have not taken you to court over the debt then the debt collector or debtor cannot sue you for that debt.
The debt is still owed but you cannot be forced to pay for the debt after 7 years.
If you cannot pay the debt then don't speak with the debt collector or make any payment arrangements with the debt collector as that restarts the clock on the 7 years.
When a debt is sold off to a debt collector the debt collector has bought your debt for pennies on the dollar and then when they try to harass you by phone, letters etc to get you to pay the debt the debt collector makes their money back when you pay even part of the debt.
However if you pay the full debt then the debt collector makes a good profit off your debt as they didn't pay the same amount of money you owed.
Also paying a debt collector does not mean your debt will be reported as paid or raise your credit score.