Brokers are only obliged to keep records for 5 years. In addition with the consolidation of the industry, agents changing offices or getting out of the business all together. It would be prudent to get everything now.
I know a big real estate franchise office near me that has digitized all their records going back over 30 years, but if you call for a copy of anything they charge you a fee for looking it up and sending it to you. I'd say they're definately one of few offices doing this, but I'd check with your broker to be sure.
Get everything in digital format as others mentioned.
get paper back up file as well .
Store it yourself, don't rely on the agent.
Agent or broker or main office will keep paper documents as long as they are legally required to then probably send it to shredder. Storage space is at a premium.
Personally I have nearly two decades of files taking up enormous space in my garage, I plan to take everything that is old dated to the shredder this summer (same plan I have every summer, but have not got around to it yet ) If I have to park my car in the driveway in the 105* Sacramento summer sun again, I might get motivated to finally do it this summer. :)