PlayStation® General

[gkpama00]

Nothing that you purchase with a Playstation Plus discount ever expires.  If you paid an additional fee beyond the subscription for content, you keep it after your subscription ends.  The only content that can expire is content that has a price listed, but is free to download for Plus subscribers.  And except for full games, you can keep even that stuff after your subscription ends.

[gkpama00]

That's what Sony says in their announcements; and based on the expiration dates listed for the content itself on the PS3, it appears to be correct.