Not really sure what you are asking or what product you are using. Are you using Dynatrace (accessing mainly through a web UI) or AppMon (accessing mainly through a rich client)? Data retention policies are different for each.
PurePath retention will be based off of the amount of disk space that is available for session storage as new PurePaths come in and there is no space available the older ones get cycled out. I'd say you have two options:
PurePaths are proprietary so there would be no way to export them to another tool, you'll need to use a client if you want to analyze any you have exported.