Most closed listings are only stored for about 90 days.
That's long enough for the most convoluted dispute to work itself out, even if an appeal is made via credit card chargeback.
However, your Paypal account will hold onto your payments sent and recieved indefinitely, although all you will see is the title of the auction, the amounts, and the other member's name.
If you need more information, you may want to print out each of your purchases and sales and keep them in binders.
Hmmm- Is the item one that you paid for but did not receive? Is the seller now "Not A Registered User"? Scamming listings are pulled as soon as eBay learns about them.