When the account reverts from VIP to Premium, access to areas (e.g. North Downs, Evendim) due to being VIP will be gone when the VIP ends. Any area that you already bought the quest pack for you will still have access to. You will still be able to complete any quest or deed that is started, but will not be able to get any new ones without either buying the quest pack or going back to VIP. Also, while you are a VIP you will not be able to buy the quest packs for the areas you get as part of being a VIP.
Side Note: The benefits that are kept when going from VIP to Premium are only for the characters that are logged into the game while a VIP. If you don't log them in while a VIP, they do not get the benefit. New characters created after VIP ends also do not have the benefits. So be sure to log in all characters while the VIP is active, even if you do not play them regularly.
"Everyone's got one. Better to be a smart one than a dumb one." - me
"It's people like you that [I]think[/I] you know everything that give those of us that [I]do[/I] a bad name." - me
"Eat, drink, and be Merry, 'cause Pippin was a fool of a Took."